Locke1980PartII

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T H E I N F E R E N C E OF S P E E C H P E R C E P T I O N IN T H E 
P H O N O L O G I C A L L Y D I S O R D E R E D C H I L D . P A R T 11: 
S O M E C L I N I C A L L Y N O V E L P R O C E D U R E S , T H E I R 
USE, S O M E F I N D I N G S 
John L. Locke 
Institute for Child Behavior a*M Development, Champaign, Illinois 
Several procedures used to assess speech perception of children with disorders at the 
phonological level of language are described. In most cases of segmental substitution, 
children discriminated target and substitution phonemes regardless of whether both 
were spoken by an adult, or one form was produced by an adult and the other was the 
child's internal representation of the target phoneme. However, in about a third of 
the cases there was consistent failure to discriminate the target phoneme from the 
substituted phoneme. Perceptual approaches to the treatment of sound production 
problems are questioned when perception is inferably differential. Certain phonetic 
effects, and their implications for theories of phonological acquisition and disorder, 
are discussed. 
In Part I of this two-part series (Locke, 1980), a rationale for the assessment of 
speech perception in children with disorders at the phonological level of language 
was presented. Essentially, our position is that speech perception deserves clinical 
interest to the extent that production difficulties are linked to problems of perceptual 
processing, and that the elicitation of perceptual responses is one of the few good 
ways of inferring what a child knows about the phonological structure of language. 
This being so, we set down some criteria for efficient assessment of speech percep- 
tion when performed for the purpose of treating a production disorder. The criteria 
are that the assessment procedure must 
(l) examine the child's perception of the replaced sound in relatiQn to the replacing 
sound, that is, the target phoneme versus its substitution phoneme, or, as in the 
case of complete omission, silence; 
(2) observe the same phonemes in identical phonetic environments in production 
and perception; 
(3) permit a comparison of the child's performance on target and replacing sounds 
with his discrimination of target and perceptually similar control sounds; 
(4) be based on a comparison of an adult's surface form and the child's own internal 
representation: 
(5) present repeated opportunities for the child to reveal his perceptual decisions; 
(6) prevent nonperceptual errors from masquerading as perceptual errors; 
(7) require a response easily within a young child's conceptual capacities and reper- 
toire of responses: and 
(8) allow a determination of the direction of misperception. 
445 
Journal of Speech and Hearing D i s o r d e r s 0022-4677-80-4504-0445501.00-0 
O 1980, American Speech-Language-Hearing Association 
446 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
In the earlier paper we then examined existing tests in relation to these criteria; we 
found that no commercially available procedures were clinically satisfactory. The 
present paper describes some clinically novel procedures that better meet the criteria 
listed above, presents data gathered with these procedures, and discusses their use 
with young children with phonological disorders. Though the several paradigms dif- 
fer, the tasks appear or iented to one or the other of two general types o f perceptual 
processing: 
Type I: Adult surface form---child's internal representation. Several procedures, 
including the conventional picture tests (for example, Templin, 1957), fit this cate- 
gory. Typically, tee child is exposed to an external referent , such as a picture or an 
object, the name of which is represented phonologically in his long-term lexical 
memory, that is, in his receptive vocabulary. The child must de termine if a heard 
sound fits an internally "imaged" category of sounds, a phonemic class. Since each 
trial requires no more than one spoken syllable, on formal grounds the Type I test 
would be relatively immune to the decay of acoustic information in sensory memory. 
The Type I test also would be relatively insensitive to allophonic discrimination, since 
the child is free to establish a criterion as to what constitutes a match between the 
tester's spoken form and the child's stored form. 
Type II: Adult surface f o r m - - a d u h surface form. There are several tests of this 
type, including the conventional same-different test (for example, Wepman's Auditory 
Discrimination Test, 1973). They require the child to make a decision with respect to 
two or more syllables heard in close succession. The child is not asked whether an 
adult form differs from his form, but whether it differs from another adul t form. 
With short intersyllabic intervals, certain Type II tests may be relatively sensitive to 
what, for the child, may be al lophonic detail. With the exception o f the same- 
different task, procedures of this type tend to br ing the listener's cri terion under the 
control of the experimenter . 
T Y P E I T E S T S 
We are aware of only two tests that fit into this category. One is the picture iden- 
tification task described in the earlier paper. For reasons detailed there, this proce- 
dure is of limited clinical usefulness and will not be discussed further. The other test 
is one developed by us. It is called the Speech Production-Perception Task (SP-PT). 
Speech Product ion -Percept ion Task 
In 1970, we set out to conduct some prel iminary studies of a task format that 
would meet all the criteria described. The task was inspired by Koenigsknecht and 
Lee (1968) (as was a procedure called the Washington Speech Sound Discrimination Test 
[Prather, 1971]). We asked kindergar teners to name pictures (for example, thumb). If 
a phoneme were omitted or replaced, we then presented the children with a series of 
stimulus-questions in which the same labels were articulated correctly (for example, is 
this /0Am/?) or incorrectly, either as the children had said them (for example, is this 
/fAmE) or in a neutral way (for example, is this /sAm/?). Our interest was in observing 
whether these subjects would accept (yes) or reject (no) the correct and incorrect 
phonemes. Most chi ldren accepted correct phonemes and rejected both forrns of in- 
:orrect phonemes. However, some accepted their own (incorrect) form, rejecting 
only the neutral (incorrect) form. All children, then, accepted correct productions 
LOCKE: Inference of Speech Perception, Part II 447 
and rejected neutral productions, with differences between subjects due exclusively 
to how they handled their own form. We could not know what the children per- 
ceived, but we were able to observe what they verbally accepted and rejected. 
These preliminary findings suggested the improbability o f observing clinically rele- 
vant production-perception relationships when the perceptual stimuli were selected 
without knowledge of, or regard to, the subject's production responses. It began to 
appear, following these observations, that the most appropriate task would be one 
that contained no pre-selected stimuli. Perhaps, by virtue of his responses in articula- 
tion testing, the child should unwittingly select his own stimuli. In that case, the clini- 
cian would need a task format into which these stimuli could be placed. The format 
we settled on appears in Figure 1. Though it does not test production, it requires and 
must immediately follow such a test; its intent is to determine the presence, and 
something about the nature of, production-perception relationships. 
Speech Production-Perception Task 
Child's Name Sex: M F Birthdate 
Date Date Date 
Production Task Production Task 
Stimulus Response Stimulus Response 
/ @ a ~ /÷£ $ ^ , ~ ] / ~ezk /+{ Wezk ] 
SP l S l Re /~'/ CP / a / SP / r / RPIwl CP / I 1 
S ~imulus-Olass Response Stimulus-Class Response 
i ISI-cP yes~ i I~I-SP ~no 
2 / "~ /-RP ~ ) NO 2 t i / -CP yes~ 
3 /e/-SE ~no 3 /~/-SP ~no 
Jei-SE ~D.o 4 J Ii-cP ye~ G 
5 /~/-~ ~NO 5 Iw/-~ ye~ 
6 1 (~/-CP yes ~ 6 /W /-RP yes 
7 /$/-CP yesQ 7 /~/-SP Qno 
8 /e/-sP ~no 8 /W/-m~ ( ~ NO 
9 I # 1 - ~ ~NO 9 l l " l - sp ~no 
lo te t -sP Y ~ o 10 / I / -cP yes(~ 
ll I*i-~ (~)NO n / I i-cP yes(~ 
12 !S l -cP yes G 12 IwI-Pm y e s ( ~ 
13 I ' ~1 -~ (~ )NO z3 I r l - s p ( ~ . o 
z4 /e/-sP ~no 14 / I t-cP yes (~ 
15 I=l l -cP yes~ 15 I w l - i ~ yes G 
16 /~/-RP yes~ 16 /~/-SP ~_~no 
17 /~/-SP ~no 17 /W/-RP yes~ 
18 / $/-CP yes~ 18 / i /-CP yes~ 
Production Task 
Stimulus Response 
/ J'~ /+[ Su~ ] 
sp ISl ~ IS/ CE I'~I 
Stimulus-Class Response 
i /~/-R~ ~ No 
2 I~ /-CP yesQ 
3 / t /-CP yes~ 
4 /~l-sP YES O 
5 IfI-sF G n o 
6 1 ~ I-RP ~NO 
7 / ~/-RP ~NO 
8 / J /-SP @no 
9 / t/-CP yes~ 
lo / ~/- sP (~)no 
ii / t I-CP yesN~ 
12 1 & I-RP QNO 
13 1 I I-SP ~.~no 
14 / ~/-RP ~NO 
Is I~ l-sP ~ o 
16 / t/-CP yes 
17 f t / - cp ~N0 
18 / .%/-RP ~ves~NO 
RP g CP O SP O RP__L CP__Q SPX~_ RE__e_ CP~ SP~__ 
Enter errors above 
Figure 1. A sample Speech Production-Perception Task form, filled in and 
hypothetically scored purely for illustrative purposes. This imaginary child gave 
evidence of misperceiving /f/-/O/ and /s/-/f/, gave no evidence of misperceiving 
fwl-lrt. 
448 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
The task form contains a sequence of unfilled phonetic brackets, stimulus classifi- 
cations, and an indication of the appropr ia te responses. The three columns provide 
for repeated observation of a single phonetic contrast or a single observation of sev- 
eral phonetic contrasts, in Figure 1, the columns have been filled in for illustrative 
purposes. 
Procedure. First the child's articulation was assessed by asking him to name pictures, 
objects, or body parts. The child's productions and the corresponding adult forms 
were then used in the percept ion task. The child's phonemic misproduct ion was en- 
tered in the brackets for Production Task Response. The typical adult American English 
pi 'oduction of the same stimulus was entered in the space for Production Task Stimulus. 
This ensured that the stimuli in product ion and perception tasks were identical and 
specified. The phoneme misarticulated was entered in SP [ ] to show that this was the 
stimulus phoneme in the percept ion assessment. The child's substitution phoneme 
was entered in R P [ ] to show that this was his er ror response. CP [ ] was reserved for 
the use of a perceptual ly similar control phoneme. The SP, RP, and CP stimuli were 
then entered in the brackets in the column below. 
Stimulus Presentation. The tester presented each stimulus live-voice with a natural 
but constant intonation pattern. Routinely, the tester sat beside the child, who was to 
look at the visual stimulus that had elicited the misarticulation. No re inforcement or 
feedback was given by the examiner, who merely asked Is this _ _ ~ etc., circled 
the child's yes or no responses, added the errors of each type, and entered the sums in 
the appropr ia te spaces at the bottom of the sheet. 
Training. Young children were given training before taking the SP-PT. The main 
reason for this was that some children saidyes indiscriminately until oriented to give 
affirmative answers selectively. For example, for the child who says [1"] for/ t j ' / , the 
tester would point to a chair and ask Is this table? Is this bear? Is this chair? Is this stair? Is 
this tare? Is this chair? The task was not begun until the child rejected perceptually 
dissimilar items such as bear, stair, and tare and accepted the correct form, chair. 
Henceforth, one expected the child to accept chair and reject the control phoneme 
(for example, tare). How the child would respond to his form (share), of course, was 
de termined from his performance. 
Task Structure. Each stimulus type was presented with equal frequency (six times) so 
that e r ror analyses could be per formed without calculating proport ions. The se- 
quence of stimuli was randomly de te rmined within the constraints that no stimulus 
type (CP, RP, SP) could occur more than twice consecutively, and that each block of 
six items (1-6, 7-12, 13-18) had to include two of each of the three types. 
The order ing and frequency of stimulus types also were sensitive to certain re- 
sponse probabilities. Since only SP items proper ly have a yes answer, and since there 
is an equal number of the three stimulus types, the ratio of no:yes responses was 2:1 
for correctly perceiving subjects. The ratio for children who accepted the response 
phoneme and rejected control phonemes was 1:2 (there can be no 1:1 ratio of no:yes 
responses because 1:1 for a normally perceiving child would be 0:2 for a misperceiv- 
ing child). The randomizat ion of stimuli was done with reference to a third criterion 
as well as the two repor ted above: no more than two yes and three no responses were 
to occur consecutively. 
Control Phonemes. Control phonemes were drawn from a table created from misper- 
ception data (Miller and Nicely, 1955; Wang and Bilger, 1974) and conventional 
phonetic taxonomies. In the table, each American English consonant (for example, 
/~/) is followed by five perceptually similar control sounds (for example, /f s p t k/). 
The sound selected for use as a control phoneme was the left-most item in the table 
LOCKE: Inference of Speech Perception, Part II 449 
(that is, the perceptual ly most similar) that was not itself involved in the child's sub- 
stitution and did not create a sensible question (for example, for the child with a O/s, 
Is this fun?). 
Administration Time. Usually, less than five minutes were needed to train a young 
child and to fill in the form for one percept ion test. The actual administrat ion time 
for an 18-item task was about one minute, paced moderately, for children's responses 
generally are initiated within one second (Forcucci, 1972). Scoring and interpreta t ion 
typically were accomplished in a minute. 
Cognitive Processing. In the SP-PT, the subject must compare information held in 
echoic memory (see Crowder, 1978) to information in long-term memory. This dif- 
fers markedly from an AX situation, in which the to-be-compared items both occupy 
echoic memory. These differences in SP-PT and AX task requirements may be im- 
portant . Consider the problems of a child acquiring phonology. In the early stages of 
acquisition the child possesses a restricted reper to i re of functional phonological units 
(Locke, in press, c). The accumulation of addit ional phonemes (via lexical acquisition) 
logically would involve a process in which the child recognizes the presence of pho- 
netic patterns that, to him, are novel. The child's phonology could not differentiate 
and e x p a n d wi thout such recogni t ion . Studies of infant pe rcep t ion show that 
stimulus pat terns are not likely to be a t tended to unless they are unlike those experi- 
enced previously (Cohen and Gelber, 1975). The determinat ion o f what is novel can 
only be made by the child as he compares recent phonetic inputs to speech categories 
in long-term memory. T h e SP-PTs requirements conform to those processing de- 
mands. In the AX task, on the other hand, the echoic storage of syllables appears 
more relevant to the percept ion of sequential information as required in the process- 
ing of polysyllabic or phrase-length utterances. 
Important ly, since there is a referent in view, the SP-PT permits one to infer 
whether the adul t surface form corresponds to the child's internal representat ion of 
that referent . That is, the child is asked, in essence, if what the clinician said is similar 
to or different from theform the child has stored in his head. This is a phonological 
question. To ask, on the other hand, if two sounds are the same or different is asking 
nothing (directly) about the phonetic or phonemic form of the child's lexical entries. 
A Caveat. Perhaps it is appropr ia te here to raise a point relevant to all percept ion 
tests. One is on reasonably safe grounds in producing a sound that can represent the 
phonemic target the child appears to be missing in his own output . This is true, at 
least, for examiners whose dialect is like that of the child's phonological community. 
One should, for similar reasons, be able to select a control sound. However, for any 
efficient test of speech percept ion we are forced to assume additionally that the ex- 
aminer is capable of producing sounds that closely resemble the child's e r ror utter- 
ances. In the case of so-called distortion errors, this assumption in many cases would 
be false. This is because listeners have no reliable perceptual boundaries for phones 
that lie outside their phonological system and no well-formed product ion routines 
either. Consequently, we could never be sure we perceived a child's distorted utter- 
ances accurately, and even if we could, there is no guarantee we could reproduce 
them to our own satisfaction, much less the child's. 
In the case o f substitution errors, the evidence to date (Locke, 1979a) is that in 
most cases our assumption would be correct and that the child would not discrimi- 
nate a product ion of an adul t ' s /w/ - -+ [w] from the chi ld ' s / r / - -+ [w]. Were this not 
true, there would be no way o f clearly in terpret ing a child's rejection of [w] in refer- 
ence to a n / r / r e f e r e n t . On the one hand, the child could reject the adult 's form, [W]A, 
because it differs from the child's form, /w/o not because it differs f rom/ r / . On the 
450 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
other hand, the child could reject the adult 's [w] because it differs from the correct 
form, /r/, which is the interpretat ion one would like to be possible. T h o u g h the 
reader is advised to consult reports of children's subphonemic cues (Macken and 
Barton, 1980 Costley and Broen, 1976; Bernthal and Weiner, 1976), there is reason 
to believe that chi ldren are not, themselves, uniformly aware Of such cues (Dodd, 
1975; Locke and Kutz, 1975; Panagos and King, 1975) to the extent that they could 
use them to discriminate adult-child differences in the product ion of the child's sub- 
stitution phoneme. The matter deser)es fur ther attention, however (see Baran and 
Seymour, 1976). 
Experience with the SP-PT. We began in 1972 to use the SP-PT in earnest and since 
then have completed the testing of 131 subjects. Thei r ages ranged from 3.1 to 9.9 
years, though only seven were 7.0 or older (X = 5.33; SD = 1.18). There were 84 
males. 
In many cases, children were tested on one or more contrasts they collapsed by 
phoneme substitution or omission (A T = 99). In other cases, they were tested solely on 
contrasts of sounds said correctly (N = 17). In still other cases, they were tested on 
both correctly and incorrectly produced contrasts (N = 15). In all, 209 phonemic 
contrasts were tested 175 involved sounds the children collapsed either by substitu- 
tion (171) or omission (4), and the other 34 involved correctly p r o d u c e d contrasts. 
By intent, chi ldren were seen by a number of different testers (N = 10) in a variety 
of professional and physical environments. Thir ty-one were enrolled in public school 
speech therapy and were tested by their clinician; none had at the time of testing 
undergone t reatment for the contrast tested. Twenty-two were public school kinder- 
garteners not enrol led in speech therapy. Sixty-six were young children enrol led in 
preschool or day-care programs, and though most of them had speech substitutions, 
they did not necessarily have a d i sorder o f speech. Twelve were enrol led in a 
Headstar t program. About a dozen were tested by the author, and he was present 
frequently. All were tested live-voice except for 18 who received the stimulus ques- 
tions from audio tape and loudspeaker. 
Since our earlier paper (Locke, 1980) questioned the propr ie ty of numerical scores, 
a misperception formula was derived that compared the child's errors on replacing 
sound with the child's errors on target and control sounds. According to the logic 
described in the previous paper , the misperceiving child might consider that his 
sound was cor rec t - -no t that the adul t form was wrong or that some neutral version 
would be correct. Tha t correctly p roduced contrasts are themselves evidence of dis- 
crimination was also assumed. Consequently, the formula was derived both logically 
and empirically; it was one never violated in the 34 cases of correctly produced con- 
trast. The formula is RP ---> 3 > 2 (SP ÷ CP), which means that there had to be at least 
three errors on the response phoneme and that response phoneme errors had to 
exceed a doubl ing of the two other kinds of errors summed. This formula was 
applied to the response patterns of all chi ldren tested henceforth, misperception is 
used only where the terms of the formula were met by the response pattern o f the 
child. 
Some response patterns that would qualify as misperceptions under the terms of 
the formula are 
RP SP CP 
6 1 0 
6 0 2 
5 1 1 
0 2 
4 0 1 
LOCKE: Inference of Speech Perception, Part II 451 
Such pat terns as the above did not occur in two genera l categories of responding . In 
one, the child had correct percept ion as indicated by the fact that he made few or no 
errors of any given type. T h e o ther cr i ter ion fai lure was due to quest ionable pat terns, 
ones in which there were large n u m b e r s of e r rors on all three s t imulus types. Twelve 
percent o f the tests were like this, and they indicate no t that the child had a percep- 
t ion p rob lem bu t that his test ing needed to be tr ied on ano the r occasion. (In one case, 
a child who said [lib] for / l i f t accepted ou r control item; [li0], which u n d o u b t e d l y was 
more similar to /lif/ t han was [lib].) Since we f requent ly were guests o f the public 
schools, we could no t in all cases resolve these inde te rmina t ions with a follow-up visit 
or a session of appropr ia te length. 
Table 1 shows the incidence of correct percept ion, mispercept ion, and quest ionable 
results for the 209 phonemic contrasts e i ther collapsed or p roduced distinctively by 
the chi ldren tested. W h e n quest ionable pat terns are coun ted as mispercept ions, the 
inc idence of mispercept ion for collapsed contrasts is 38.9%. W h e n quest ionable pat- 
terns are coun ted as correct perceptions, the co r r e spond ing incidence of mispercep- 
t ion is 26.9%. 
TABLE 1. Speech Production-Perception Task results on 131 children tested on 209 contrasts. 
Phonemically Collapsed Phonemically Distinctive 
correct misperception question correct misperception question 
stop-stop 5 1 1 1 0 0 
stop-fricative 7 0 1 2 0 0 
stop-affricate 1 0 0 
fricative-affricate 5 3 1 
fricative-fricative 38 42 8 20 0 1 
f/0 (12) (35) (5) (12) (0) (0) 
O/S.s/O t (16) (4) (3) ( 1 ) (0) (0) 
s/St fls" (7) (3) (0) (4) (0) (1) 
s/z (3) (0) (0) (3) (0) (0) 
liquid-liquid (l/r) 1 0 0 
glide-liquid 45 1 7 10 0 0 
w/r (37) (0) (6) (7) (0) (0) 
w/l (8) (1) (1) (3) (0) (0) 
segment-deletion 3 0 1 
other (e.g., d/f) 2 0 2 
Total 107 47 21 33 0 1 
Percent 61.1 26.9 12.0 97.1 0.0 2.9 
Between 27% and 39% of the misp roduced contrasts were misperceived, bu t did 
this apply equally across phonemic opposi t ions? H a r d l y - - a l t h o u g h 49% of the con- 
trasts had a voiceless fricative as both the s t imulusand the response phoneme, these 
cases accounted for 89% of the misperceptions. T h e r e was no mispercept ion o f /w- r / 
contrasts, bu t there was a 67% incidence of mispercept ion w h e n / f - 0 / w a s tested. T h e 
only mispercept ions not involving at least one fricative occurred on a /w- l / con t r a s t in 
one case and a / g - d / c o n t r a s t in another . O f the 34 cases in which the contrast was 
p roduced correctly, 33 were perceived differential ly with jus t one quest ionable pat- 
tern. 
452 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
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LOCKE: Inference of Speech Perception, Part II 453 
The high incidence o f / i f #0 /mi spe rcep t i on was associated with chronological age. 
Of the 52 children who said [f] for /0/ in initial or final position, the 26 younger 
subjects (Range: 3.1-5.5; Mean: 3.7) were considerably more likely to misperceive 
than the 26 older chi ldren (Range: 5.6-8.1; Mean: 6.2). The re were 22 (85%) in the 
younger group who met the criterion for misperception, as compared to 13 (50%) in 
the o lder g roup who were classified as misperceivers. While o lder and younger 
groups had similar mean errors on SP and CP items combined (0.46 and 0.50, re- 
spectively), older subjects commit ted fewer errors on RP items (3.08/6) than younger 
children (5.00/6), a significant difference (t = 3.089; p < 0.01). 
We have spoken of contrasts being misperceived instead of chi ldren who were mis- 
perceivers. The terms were not selected capriciously. Table 2 is a listing of subjects 
who were tested on both a correctly and an incorrectly produced contrast. In all 
cases, the phonemic contrast on the r ight of the Table was produced correctly by the 
child, and the contrast on the left was collapsed in the child's speech. Note that sub- 
jects 78, 79, 80, and 81 produced a phonemic substitution in one syllabic position but 
not in another. The correct percept ion of these subjects corresponds with the chil- 
dren 's correct production, jus t as they were observed to misperceive sounds they 
misproduced (though Subject 80 produced a questionable pat tern on /s-J'/ finally). 
The other subjects were tested on different contrasts but in the same syllable posi- 
tion. This was to ensure that product ion- l inked variations in percept ion were not due 
to a confounding of articulation and syllable position. They were not, as Table 2 
shows for Subjects 27, 63, 78, 104, and 114. This is also apparen t in Table 3, which 
shows the incidence of correct and incorrect percept ion as a function of phonemic 
contrast and syllable position. Excluding questionable patterns, initial sounds are 
misperceived in 51% of the cases as opposed to 41.7% misperception of final con- 
trasts. Much o f this difference is due, however, to the unequal discriminability of if-0/ 
contrasts in initial and final position; i f -0/was misperceived in 71% of the syllable- 
initial cases and in 58% of the syllable-final cases. 
TABLE 3. Perception as a function of syllable position. 
II 
Syllable initial Syllable final 
Correct Misperceived Question Correc t Misperceived Question 
f/0 5 25 5 6 9 2 
0/s 13 2 0 2 1 0 
s/0 1 1 1 0 0 2 
t f/J" 1 0 0 1 0 0 
t/0 0 0 1 1 0 0 
Percent 36.4 51.0 12.7 41.7 41.7 16.7 
From a clinical viewpoint, the difficulty of discriminating /f/-/0/ may be of little 
consequence, for the articulations involved are visible and manipulable. The re are 
nonpercep tua l techniques (for example , direct physical manipula t ion of the ar- 
ticulators) for discouraging the substitution of [f] and for establishing the correct 
product ion of /0 / . In other words, "discrimination failure" need not translate into 
"clinical problem." Presumably, a correct product ion so established would lead, even- 
tually, to correct discrimination of / f / - /0 /pa t te rns because of their association with the 
dissimilar articulatory routines fo r / f / and /O / . T h o u g h the theoretical basis for such a 
454 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445--468 November 1980 
predict ion is well established (see Winitz, 1969; Locke, 1968), this empir ical point 
needs to be conf i rmed. 
Ironically, one can imagine clinicians be ing d isappoin ted that ou r subjects dis- 
c r iminated so consistently the relatively less visible and manipu lab le tokens o f / r / , 
Disappointed, we say, because in such cases a perceptual approach is no t indicated, 
and the nonpercep tua l routes to c o r r e c t / r / p r o d u c t i o n are less s t ra ightforward t han 
in the case of /0 / . Since in cases of correct percept ion the child apparen t ly has the 
adul t surface f~orm as his in te rna l representa t ion , the failure to achieve or express 
that represen ta t ion seems to be due to problems at the o u t p u t level or in the l inking 
strategies a n d rules that media te the child 's i n t e rna l r ep re sen t a t i on and o u t p u t 
(Smith, 1979). How one deals with problems at these levels is not obvious. 
We have m e n t i o n e d a c r i t e r i o n - o r at least a desireable f e a t u r e - o f a discr imina- 
t ion task, the detect ion of unid i rec t ional d iscr iminat ion failure. Little is known about 
the directionali ty of d iscr iminat ion errors (probably because the much used AX task 
does not permi t directionali ty analysis), bu t it has been cons idered impor t an t that 
such a de t e rmina t ion be achievable since product ion errors typically are skewed. We 
tested 40 chi ldren with phonemic subst i tut ions "both ways." First we used a picture or 
object to represen t the target p h o n e m e (for example, rake) and asked Is this [reik]? Is 
this [weik]? Is this [leik]? and so on, W h e n the test ing was completed, we then pre- 
sented the child with a picture or object to represen t the subst i tut ion p h o n e m e (for 
example, wake), which was said correctly, asking is this [reik]? Is this [weik]? Is this 
[leik]? Of the 53 three- to six-year-olds tested in this fashion, 37 had correct percep- 
t ion a n d 16 had mispercept ion when the misp roduced sound served as the s t imulus 
phoneme. Table 4 shows that in 13 of the 16 cases, the chi ldren gave similar evidence 
TABLE 4. Speech Production-Perception Task errors when the picture's name contained the 
stimulus phoneme (e.g.,/0/, the sound the child replaced) and the response phoneme (e.g.,/f/, 
the child's replacing sound). 
I I I I II I I I I I II II I I I I I I 
Picture's Name Containing: 
Stimulus Phonemet Response Phoneme 
Subject Sex Age Substitution SP( O) RP(J) CP(s) SP09 RP( O) CP(s) 
14 M 3.9 f/0 0 6 0 0 4 0 
22 M 4.10 f/0 0 6 0 0 6 0 
23 M 5.2 f/0 1 4 0 1 3 3 
24 M 3.10 f/0 0 4 1 0 4 3 
27 F 5.5 f/0 0 5 0 0 6 0 
103" M 4.7 f/0 1 6 0 2 6 0 
103" . . . . w/r 1 5 I 1 0 0 
110" M 3.1 f/0 0 7 2 0 4 0 
203* M 4.5 0/s 0 6 0 0 4 0 
206* M 4.1 f/0 0 7 0 0 8 0 
301" M 4.5 f/0 0 6 0 0 6 0 
303* M 5.0 f/0 1 5 0 0 7 0 
407 M 5.0 f/0 0 6 0 1 3 1 
408 M 5.0 f/0 0 6 0 5 1 0 
412 M 4.0 f/0 0 6 0 0 6 0 
415 M 4.0 J'/tJ" 0 5 0 0 5 1 
I I I I I 
t/0/, If/, and Is/are used here to exemplify the SP, RP, and CP categories. For Subjects 103, 
203, and 415, the SP, RP, and CP were/r/-/w/-/l/,/s/-/O/-/f/, and/tS/-/f/-/t/, respectively. 
*Tested on eight SP, RP, and CP items (all others tested on six). 
LOCKE: Inference of Speech Perception, Part II 455 
of misperception when their substitutions were treated as the stimulus phonemes. 
Consequently, most of the children tested here seemed to have a single internal rep- 
resentation for both the adul t /0 /and/ f / , each expressed as If] (as did Broen and Jons ' 
[in press] voiced/voiceless child err bidirectionally on a picture identification task, 
according to their anecdotal accoun D. One could thenquestion, as several people 
have (for example, Compton, 1970), why the child has chosen to represent the two 
phonemes invariantly with phones adults use to represent just one o f the phonemes. 
Said another way, if the child cannot tell X from Y, why does he/she always say X for 
Y, and never Y for X? One answer is that the behavior probably was motivated by 
perceptual factors working in conjunction with product ion factors, as has been 
theorized elsewhere (Locke, in press, a). 
We also have in Table 4, however, the patterns o f Subject 103. He said w/r and 
indicated, five out of six times, that [weik] was an acceptable name for rake. He did 
not, however, think that [reik] was an acceptable name for wake. Apparently, this 
four-year-old boy was implying that he could tell [r] f rom/w/even if he could not tell 
[w] from/r/ . The same child did a somewhat different thing with if-0/, indicating that 
[f] could represent /0 /about as well as [0] could represent/f/ . It is not clear whether 
this difference is due to the differential discriminability of /w-r /and/f -0 / , to dissimilar 
stages of phonological acquisition of the two contrasts, or to some other factor(s). 
However, we were privileged to witness a similar (perhaps) phenomenon with a five- 
year-old boy who said [fred] for/0red/ . First we gave him the SP-PT, then a picture 
identification task (with a boy designated as Fred and a spool of thread, with five trials 
on each in random order), and finally we readministered the SP-PT and the picture 
task. The errors were as follow: 
SP-PT Picture Task 
Sequence 0red fred sred Sequence 0red fred 
1 st 0 6 1 2nd 1 0 
3rd 0 0 0 4th 0 0 
As may be seen in the contrast between the first and third administrations of the 
SP-PT, the child's misperception disappeared, with only a 10-item picture identifica- 
tion task intervening. 
This sort of contrastive testing may be exploited to clinical advantage, conceivably 
replacing discrimination training with a kind of phonological reorganization (or 
reorientation). Because of other data showing that children are perfectly able to re- 
ject untargeted alternatives (as in not wabbit, wabbit.t-see Locke, 1979, a), it may be 
possible to induce certain children to reject such questions as Did you say? [0IrJg~] 
following the f/0 child's correct naming offinger. This area needs clinical study. 
The characteristic finding of this study was that substitutigns were not misper- 
ceived by their perpetrators. When a child evidences correct discrimination on the 
SP-PT, one can see little reason why it would be clinically useful to proceed upon a 
therapeutic regimen in which the child is bombarded with sound. In fact, there is 
good reason to avoid extreme--saturating--levels of phonetic stimulation; they may 
induce phonetic illusions (Warren, 1968) and the shifting of perceptual boundaries 
away from the target stimulus (Cooper, 1974). A more reasonable alternative is to 
proceed with an attempt to do something about the way the child talks. If the child 
has the right, or at least distinct, targets to shoot for, the clinician seems to risk doing 
less for him perceptually than to him. For example, the child could be confused into 
thinking that his internal representations are wrong, which would be clinically disas- 
456 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
trous, considering that in about 70% of the cases reported here one may infer they 
were not wrong. 
T Y P E 11 D I S C R I M I N A T I O N T E S T S 
Earlier we commented that the more desirable kind of discrimination required the 
child to compare an adult's surface form with the child's internally represented form. 
That was considered desirable because phonological acquisition requires that the 
child process recently heard sounds in relation to his receptive repertoire. Those that 
do not match would, by definition, be novel, and worthy of the sort of mimicry that 
encourages their incorporation into the child's expressive phonology. The child can- 
not, however, acquire distinctive internal representations without, in some sense, no- 
ticing differences at an early stage of phonetic perception. It becomes interesting to 
ask, then, if the child is able to discriminate one adult surface form from another 
adult surface form. 
In asking this question, one might tap a somewhat independent level of perceptual 
processing. Consider the language and cognition study by Brown and Horowitz (in 
Brown and Lenneberg, 1958). They attempted to train color-nonsense syllable as- 
sociations in native speakers of English and Navaho. The syl lables /ma/and/mo/were 
contrastive in both languages, but a variation in length ( /ma/vs . /ma: / ; /mo/vs . /mo: / ) 
was contrastive only in Navaho. The Navaho subjects learned color associations to all 
four syllables while their English-speaking counterparts were able to learn color as- 
sociations only to the phonemically contrastive/maJ-/mo/syllables. The experimenters 
then told the Americans that there were not just two syllables, but four, 
. . . and found, when they did so, that the English-speaking subjects started 
to pay attention to the vowel change. Many of them then remarked that they 
had noticed the variations of length at the start but had assumed they were 
accidental. The Navahos never thought of these variations as accidental. 
Both groups were perfectly able to hear the difference in question. Appar- 
ently, this test does not demonstrate a difference of auditory acuity in two 
societies but rather a difference in the range of potentially discriminable 
speech sounds customarily treated as equivalent. (p. 12) 
Every language "customarily treats as equivalent" a great many phonetic nuances. 
In fact, phonetic differences become nuances mostly by their failure to be called on 
by the language to distinguish words. As Schvachkin (1973) and Menn (1976) have 
pointed out, phonologically contrastive cues are not necessarily more gross than sub- 
phonemic variations. Would anyone wish to argue that [baet]-[baek] are perceptually 
more different than [baet]-[baeth]? Nevertheless, the first contrast is -emic in English 
and the other -etic or allophonic. 
Before learning the full range of contrasts required to differentially produce Eng- 
lish words, the child might, with justification, regard the [1]-[}] contrast as more im- 
portant than the [r]-[w] opposition, as one child apparently did (Menn, 1976). During 
this period of hypothesizing, the child consistently is saying [w] in place of / r / ; he is 
"customarily treating them as equivalent." Why, then, should the child not ignore 
their differences in the adult's speech as he does in his own? 
Speech sounds can be perceptually analyzed at several different levels (see Locke, 
in press, b); the clinical challenge is to separate the child who cannot detect a dif- 
ference between two sounds from the child who detects a difference that he considers 
linguistically unimportant and not, therefore, worth mentioning. If test procedures 
permitted the examiner to appreciate such a distinction, how could this advance the 
LOCKE: Inference of Speech Perception, Part II 457 
child's training? It could do so by identifying the child's problem as one requir ing 
discrimination training, that is, t raining in the detection of a difference not previ- 
ously known about. On the other hand, it could suggest the need not of discrimina- 
tion training but o f phonological reorganization. The distinction is not unlike one 
commonly drawn on the product ion side, the issue of stimulability. After a produc- 
tion test, one is likely to hear the clinician say This child does not make/X/; I wonder if he 
can make it? To a degree, Type II tests may ask a similar question of the child's 
perceptual behavior. I f designed properly, they meet all the criteria listed earl ier 
except two: they are not based on a comparisonof an adult 's surface form and the 
child's own internal representat ion, and they do not allow a determinat ion of the 
direction o f misperception. 
ABX Test 
Description. The ABX test has been used in numerous laboratory investigations, 
including most of the speech percept ion studies at Haskins Laboratories. As several 
investigators have pointed out (Pisoni, 1971; Barclay, 1972), the Haskins finding that 
stop consonants are pcrc~! d categorically, and vowels continuously, is a product 
primari ly of the ABX test. 
In the ABX test, the listener hears three syllables. The first two syllables are dif- 
ferent and the final syllable is identical to one of the earl ier two. Hence, the two 
possible orders are ABA (for example , / pa ba pa/) and ABB (for example , / pa ba ba/). 
The subject is to indicate whether the final or comparison syllable (X) is more like A 
or more like B. To unders tand this task and how it relates to several other perception 
tests, consider briefly what has been learned about the percept ion of speech using the 
ABX procedure. 
Some Laboratory Results from the ABX Task. In the Haskins studies, the listener usually 
is presented with individual elements from a continuous series of synthetic speech 
syllables. For example, in the study of place of articulation cues, the listener hears a 
syllable drawn from a dozen or so that differ only in the direction and extent of the 
second f o r m a n t t rans i t ion , o f ten a cr i t ical place cue. Because the s t imuli are 
Computer-generated, each syllable in the series may be equidistant acoustically from 
those that immediately precede and follow it. Hence, at one end of the cont inuum 
the listener may hea r /ba / , at the other e n d / g a / , w i t h / d a / p e r c e i v e d at some point 
in-between. Typica l ly , the subject first works th rough an identification task in which 
he labels each syllable, heard in r andom sequence, as /ba/, /da/, or /ga/. This task 
nearly always shows that the acoustic cont inuum is divided by the listener into three 
sharply def ined phonemic categories. The listener then is presented with the same 
syllables in an ABX test, which seeks to define whether his discrimination is more 
acute at his phonemic boundar ies than within his phoneme classes. For stop conso- 
nants, l isteners typically e r r at r a n d o m ~ ~en the ABX tr iad contains elements 
selected from a phonemic class and do much better when the elements span two 
phonemic classes. This is true even though the physical-energy steps are of equal 
magni tude in both cases. Therefore , consonant discrimination may be said to reflect 
a categorical or phonemic kind o f processing. Vowels tend to be perceived in a more 
continuous way, undergo ing a more audi tory kind of processing (see Blumstein, in 
press, on the invariance of consonantal audi tory cues). 
Cognitive Processing. The importance of the foregoing is that listeners in an ABX 
test typically seem to miss acoustic variations unless those variations alter the conso- 
nantal class of the sound as def ined by the listeners themselves. Recently, several 
458 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
investigators (Barclay, 1972; Pisoni and Lazarus, 1974; Pisoni and Tash, 1974) asked 
whether such categorical perception was a characteristic of the perceptual mechanism 
or a product of the test. They considered that at an early stage in the perceptual 
process, the stimulus could be analyzed auditorially--with fine acoustic nuances 
detec ted--and at later stages could only be analyzed phonemically because minor 
acoustic detail was no longer available to the subject. Barclay (1972) conceived of the 
process as follows: 
. . . the stimuli might well be perceived continuously (indicating a stage in speech 
processing in which allophone-specific information in the signal is briefly available to 
conscious inspection) and then stored categorically as phonemes . . . If the memory 
code is, in part, an articulatory code, some of the information which does not fit this 
code will be quickly lost by the listener. It appears that information specifying a par- 
ticular acoustic version of a consonant may be lost in this way, while the consonant 
itself is retained in the articulatory code. (p. 273) 
What this account is suggesting is that the listener might he able to discriminate 
more accurately if he were somehow able to act on acoustic information in this ear- 
liest stage• The clinical significance of this is that, using the ABX test, the listener may 
not be able to do that. Consider that the subject 
• . . is not making a single judgment, as good psychophysical practice usually requires, 
but a compound one. He first has the opportunity to compare B with A and probably 
always does make this comparison; then he compares X with B; then he has to reach 
back in time, so to speak, and compare X with A; and finally he has to make his 
judgment of whether the XB or XA comparison is minimal (Harris, 1952). 
If ABX testing places too heavy a burden on the listener's memory for allophonic 
detail, it may, then, invite a perception performed on a recoded version of the origi- 
nal acoustic information. As Barclay (1972) suggested, this new code into which 
acoustic information is translated probably is an articulatory (motor) one, a presump- 
tion supported by several forms of evidence (Cheng, 1973; Crowder and Morton, 
1969; Hintzman, 1967; Locke and Kutz, 1975). 
Clinical Potential• Consider a child who collapses two phonemes into a single class. 
What for the child would be a between-class d iscr imina t ion- - i f he had normal 
speech--might now have to be performed as a within-class discrimination. According 
to Barclay's (1972) conception, for a fraction of a second following the acoustic input, 
the child could hear the allophonic detail that he must rely on. With the second 
stimulus, and then the third, however, the child recodes that allophonic information 
into his articulatory system. To the extent that a task encourages articulatory recod- 
ing, so might we expect a phonologically disordered child to misperceive. 
Why, then, are we considering this task here? First, if a child does articulatorally 
recode acoustic information taken in over just several seconds' time, and responds 
with the predictable misperceptions on the ABX task, this is clinically useful informa- 
tion. Secondly, as Pisoni (1971) pointed out, 
• . . the ABX procedure has one important advantage over the traditional procedures 
such as the method of constant stimulus differences, the AX test. The listener need 
not concern himself with the nature of the differences between the stimuli. (p• 47) 
In the AX task, the criterion for the child's performance is entirely under his con- 
trol. In the ABX test, however, the child may hear three sounds that he regards as 
functionally identical (that is, phonemically unitary). The child has to make a deci- 
sion, though, as to which syllable the final one is more like. If any allophonic detail 
LOCKE: Inference of Speech Perception, Part II 459 
survives the complexities and temporal course of ABX processing, the child appar- 
endy would have to predicate his decision on whatever discriminable information is 
available, not on what he regards as important . 
The re have been several studies of children's speech percept ion that used the ABX 
procedure (Briere, 1967; Rudegeair , 1970). (A procedure called the Oliphant Auditory 
Discrimination Memory Test (1971), a g roup screening test of audi tory perceptual 
abilities, also employs the ABX format.) In Rudegeair 's study, first grade subjects 
heard the first syllable f rom a loudspeaker situated to their left, the second from a 
speaker to their right, and the comparison syllable from both speakers. The subjects 
had merely to point to the correct loudspeaker. Rudegeair 's first graders obtained 
approximate ly a 9% er ror rate for stop consonants and a 13% rate for fricatives. 
ABX Structure for Clinical Use. There are, minimally, four ar rangements of stimulus 
items in an ABX task. In the clinic, when two phonemic contrasts are used, one 
involving the target (T) with the substitution (S) phoneme and one involving the 
t a r g e t pai red with a control sound (C), the ABX task must have at least 8 items: 
T S T T C T 
T S S T C C 
S T T C T T 
S T S C T C 
With two of each, the resulting 16-item task (sequenced so that the correct response 
varies in some random or quasi- random pattern) usually can be adminis tered in sev- 
eral minutes. 
Clinical Administration. The delivery of ABX stimuli by audio recordings is impracti- 
cal for clinical use because one would need a tape p repared in advance with the 
appropr ia te contrasts in their p roper phonetic environments. Doing the ABX w i t h 
puppets or even one's bare hands is easy, however. After explaining that the hands 
will talk, the tester first makes one hand "say" one sound, then the other hand "says" 
the contrasting sound, and the speaker, with hands motionless, simply looks at the 
child and says Who said 9 The child points to the correct hand. 
T h o u g h the child needs a little orientation, dur ing which the exper imenter should 
use neutral and easy contrasts ( / u / - / i / Who said/u/?, etc.), the task is so simple that 
three-year-olds (the youngest we have tested with it) generally have no difficulty re- 
sponding to the control contrasts. 
Preliminary Results. We used an ABX test with a colorful puppe t on each hand to 
test 10 children whose ages ranged from 3.10 to 6.3 (X = 4.10). There were 10 T-S 
and 10 T-C contrasts on the test. The results are shown in Table 5. We did not 
anticipate the responses that appear in columns 6 and 8, that is, cases in which the 
child spontaneously exclaimed They both did (TBD) to a query as to which puppe t had 
said a part icular sound. This seems to be fairly s traightforward evidence that the 
child could not, at the operat ive level of processing, hear differences among the test 
stimuli. Note, however, that Subjects 21 and 28 produced some of these TBDs and 
one or two of the conventional errors as well. Left to themselves, these children 
would have pre fe r red to give TBD answers. The exper imente r was instructed to elicit 
a commitment if possible; in the TBD cases she could not. 
Subject 17 is of some concern because he missed nearly half the T-C items. Con- 
sider, however, that his T-S contrast involves /s-0/. This child received if-0/ for his 
control contrast; if-0/ is a much more difficult discrimination (child e r ror rates for 
/ f -0/were six times greater than those f o r / s - 0 / i n Graham and House, 1971). Other- 
wise, the responses of chi ldren on control contrasts appear to indicate differential 
460 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
TABLE 5. Results on a 20-item ABX task with 10 children. 
Subject Sex Age Substitution 
Target-Substitution Target-Control 
(Trials = 10) (Trials = 10) 
Error "TBD"* Error "TBD" 
15 M 4.6 t/0 4 0 1 0 
16 M 4.4 f/0 2 0 0 0 
17 M 4.6 s/0 7 0 4 0 
19 F 5.8 f/0 0 8 0 0 
21 F 4.8 f/0 1 5 0 0 
24 M 3.10 f/0 0 5 0 2 
25 F 5.4 r/r? 0 0 2 0 
26 M 5.2 0/07 1 0 2 0 
27 F 5.5 f/0 5 0 1 0 
28 F 6.3 0/01" 2 4 2 0 
*They both did, an uninstructed response that spontaneously occurred, in the cases indicated, 
when the child was asked Who said ? 
?Child was tested on if-0/or/w-r/even though his production of the sounds was correct. 
perception. The correctly produced contrasts of Subjects 25 and 26 also appear to 
have been correctly perceived; this is not so easily said of Subject 28. If he had been 
forced to commit himself, he would have missed 4/10--assuming his guessing to be 
50% correct, a chance performance. Again we have a case in which if-0/ is missed 
more frequently than /s-0/, even though production was differential in both cases. 
Better production than perception has been observed elsewhere (McReynolds, Kohn, 
and Williams, 1975; Eilers and Oller, 1976); it is theoretically troublesome, though 
Schvachkin (1973) suggested that correct production was a necessary precondition to 
correct perception, an idea not without empirical support (Briere, 1966; Broen and 
Jons, in press). 
O d d i t y Task 
Closely related to our interest in ABX testing is a concern with a related measure, 
oddity testing. Unlike ABX, oddity has been used in laboratory studies infrequently 
(Mattingly, Liberman, Syrdal, and Halwes, 1971; McGovern and Strange, 1977). 
Description• Stimulus sequences in oddity testing are very much like those used in 
ABX. There are three syllables, two the same and one different. However, in oddity 
testing, the different syllable can be the third one (in which in ABX the different 
syllable always is the first or the second). This additional privilege is possible because 
oddity tests require the subject only to indicate which of the three syllables is dif- 
ferent from the other two. 
Cognitive Processing. Concerns expressed earlier about the memory loss obtaining in 
ABX testing also are relevant here. As Barclay (1972) put it, the 
• . . use of the ABX and oddity techniques measures only successive discrimination. 
Thus, within a given trial, the listener must compare what he hears with what he 
remembers having heard a short time before. It follows that a listener's capacity for 
discrimination will be impaired to the extent that perceived acoustic information is 
lost or distorted during the interstimulus interval. (p. 269) 
The subject's strategy is likely to be somewhat different in oddity testing. In ABX 
the subject knows that the first two stimuli have to be different; hence he must hold 
LOCKE: Inference of Speech Perception, Part II 461 
them in memory long enough to find out which one the final e lement is more like. In 
oddity triads, the differ ing element can be any one of the three syllables. Of course, 
the listener has no contrastive information available when the first syllable arrives. I f 
the second differs from the first, as can be de te rmined in much the same way as in 
the conventional AX task, then he must still ask, nearly as in the ABX test, which of 
the two the final syllable is more like. However, if the first two appear identical, the 
subject can predict that the final e lement will be the different one. 
Clinical Potential. Although the contrasts appear less direct and explicit in oddity 
testing (that is, the subject never is asked w h e t h e r / w / i s more l i k e / w / t h a n it is like 
/r/), it is difficult to see why it would not furnish much the same information. 
We have used an oddity format with five day-care chi ldren whose ages were 4.3- 
5.1 years. The stimulus contrasts were fairly gross (pig-zig) and per formance was well 
above chance (84%). In testing, we simply pointed to three objects while producing 
the three syllables, working from the child's left to his right. The child merely 
pointed to the object we had been point ing to at the time the different syllable was 
produced. Nevertheless, the ABX test appears easier to instruct and to use, and as we 
said before, its comparisons seem to be more direct. 
4 l A X Task 
Not long ago, Pisoni (1971) used a new procedure to obtain discrimination data 
from adults. This p rocedure is t e rmed the 4IAX, or four-interval AX test. It appears 
to have some allophonic sensitivity and has been analyzed in comparison with the 
ABX test. 
Description. In 4IAX testing, the subject hears two pairs of syllables; one always is 
the same, the other always is different. Hence, the subject can hear AA-AB, AA-BA, 
AB-AA, or BA-AA, indicating simply whether the members of the first pair are more 
nearly alike or whetherthe members of the second pair are more nearly alike. In 
Pisoni's work (1971), an intrapair interval of 150 msec and a between-pair interval o f 
o n e sec w e r e u s e d . 
Cognitive Processing. Pisoni and Lazarus (1974) used 4IAX and ABX tests with 
adults who discriminated seven degrees of voice-onset time cutback in synthetic sylla- 
bles ranging perceptual ly f r o m / b a / t o / p a / . The 4IAX test showed significantly more 
accurate discrimination than the ABX test, especially within phonemic categories 
(where ABX discrimination usually is at chance). 
ABX and 4IAX tests share one particularly valuable p rope r ty - - t he subject cannot 
use his own criterion as in the AX test; however, the criterion need not be specified 
for him either. Precisely what is meant by same and different is built directly into the 
test; the subject is told in advance that the members o f one pair are exactly the same 
and the members of the other pair are not exactly the same. A proper ty of the 4 IAX 
test not shared by the ABX procedure is that the subject, in the 4IAX format, may 
make direct comparisons of the relevant contrasts and compare his impression from 
t h e first pair with his impression from the second. 1 This proper ty is an advantage not 
only with respect to the j u d g m e n t we wish the subject to make, but it probably re - 
~There also is an AXB format that is said to incorporate certain features of both ABX and 
4IAX schemes in that it uses three syllables per trial but requires a comparison of adjacent 
syllables. In the four possible trials (AAB, BAA, ABB, BBA), the listener is to determine 
whether the second syllable is more like the first or the third. Though the AXB has been seen to 
encourage allophonic discrimination (Donald, 1978), it has not been compared with ABX and 
4IAX procedures. 
462 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
duces some of the memory failure of ABX testing. Pisoni, in his earlier work (1971), 
reasoned that 
• .. in the ABX test, the S [subject] compares X with B and then X with A before 
arriving at a final decision. The procedure requires the S to retain information about 
the acoustic properties of the stimuli over a relative long period of time. On the other 
hand, in the 4IAX test., the S can base his final decision on a pair-wise comparison and 
respond to the magnitude of the difference between pairs of stimuli. The information 
that is retained over time for a final discrimination judgment will most probably be 
information about a decision or an evaluation such as degree of similarity on the first 
pair of stimuli (i.e., a judgment about the absolute magnitude of individual stimuli). It 
would appear from these results that retention of information about an initial decision 
(i.e., "same" or "different") is more reliable for the final discrimination judgment than 
retention of information about the specific properties of the acoustic stimuli. (p. 52) 
Clinical Potential. Earlier, we pointed out that 4IAX testing particularly facilitates 
within-phoneme discrimination. This is precisely the type of discrimination we wish 
to observe in misarticulating children. Imagine a child who has just taken a discrimi- 
nation test of the conventional AX type. Assume that he reported that /wa-wa/were 
the same and, at some other point in the test, also reported that /wa-ra/were the 
same. Now imagine this child working a 4IAX task in which he is presented/wa-wa/ - 
/wa-ra/ and is asked in which of the two pairs the sounds are more alike. That he 
thought both were the same earlier will not do here. Maybe they both were the same 
earlier, according to the criterion used then, but now one syllable pair has to be 
"more same" than the other. As in none of the other tasks, the 4IAX procedure 
appears to provide the subject with a clear perceptual reference for sameness. 
Results on the 4IAX Task. Forty-five four- to six-year-old preschool and day-care 
children were tested on 75 phonemic contrasts, 28 involving sounds substituted by 
the ch i ld ren , 47 involving sounds said correctly. The task c o n t a i n e d eight T-S 
(Target-Substitution; for example, w-r - r-r) and eight T-C (Target-Control; for 
example, 1-r - r-r) items in quasi-random order. On each trial, two syllable pairs were 
produced by the experimenter live-voice through the medium of colorful puppets. 
First, one puppet would "speak" (for example, wing-ring), then the other .(for exam- 
ple, ring-ring), and the child would be asked Who said "same sounds"? 
As in ABX testing, there were some cases of children responding They both did. In 
the analysis below, these cases were assigned half-credit on the assumption that had 
the children been forced to guess they would have been correct half the time (the 
correct answer was on the right and left equally often). Seven of the 45 children gave 
a both did response at least once. All seven cases involved the testing of a substitution 
item, and in six of the seven cases the both did response was to a T-S stimulus. We 
have no way of knowing, of course, how many incorrect and correct responses actu- 
ally were guesses nor how many both dids would have eventuated in correct pointings 
had the children been persuaded to guess. 
A formula for misperception was derived by inspecting the data from correctly 
produced contrasts. A phonemic contrast was considered to have been misperceived 
when T-S errors were at least three and when the T-S - T-C difference was at least 
three. Some patterns that would have been considered misperception were 3-0, 4-1, 
5-2, and so forth, on T-S and T-C contrasts, respectively. 
There were 14 cases of w/r. Only one of these cases was misperceived (T-S:6; 
T-C:2), and the mean error for T-S and T-C cases was 1.00 and 0.54, as Table 6 
indicates. Of the 24 r/r's tested (that is, correct/r/s), none were misperceived, and the 
mean error for T-S and T-C cases was 0.96 and 0.63, respectively. 
There were nine f/8 cases tested. As many as five may have been misperceived 
LOCKE: Inference of Speech Perception, Part II 463 
TABLE 6.4IAX task errors of 45 four- to six-year-olds on 75 phonemic contrasts. 
Target-Substitution Target-Control Number of Cases 
Substitution (Trials = 8) (Trials = 8) of Misperception 
w/r (N = 14) 1.00 0.54 1 
r/r (N = 24) 0.95 0.63 0 
f/0 (N = 9) 3.56 0.22 5 
0/s (N = 4) 0.75 0.75 0 
0/0 (N = 23) 1.95 0.70 4 
t/0 (N = 1) (3) (0) 1 
(with individual scores ranging from 3-0 to 8-0), and the mean T-S and T-C scores 
were 3,56 and 0.22. There were four 0/s cases, none of which were misperceived. 
Four of the 23 cor rec t /0 /product ions tested may have been misperceived (with/f/), 
the scores varying from 3-0 to 4-0. These control cases had a mean error of 1.95 and 
0.70 for T-S and T-C contrasts. 
Two things are clear from the analysis of 4IAX data: f/e cases were commonly 
misperceived and w/r cases were misperceived rarely. In general, the findings look 
little different from the results of ABX, AX, and P-P tests. Consequently, we will look 
now at the results of those few children who took all four tests. 
I N T E R T A S K C O M P A R I S O N S 
Fourteen children received at least three of the four tests in quasi-random order, 
each administered as described earlier. The AX task had four each of T-S and T-C 
contrasts and eight noncontrastive pairs. The experimenter made a puppet speak 
both syllables and asked the child Did he say "same sounds"? The child was merely to 
answeryes or no, a procedure that seems to work better with young children than the 
conventionalsame/different response. In nearly all cases, the words used were the same 
in all four tasks. Table 7 shows the results, with the total possible errors at the top of 
each column. 
An inspection of these data seems to indicate little variation across the several tasks, 
with two possible exceptions. Subject 16 appears to havemisperceived on the SP-PT, 
the AX task, and 4IAX task, but not on the ABX. However, this four-year-old boy 
received the ABX test last, and since we have not given one procedure as many as 
four times to the same child--testing the same contrast each t ime--we cannot rule 
out the possibility that his improvement was due to accumulated experiences in hav- 
ing to d i sc r imina te / f / - /0 / so many times in so many different ways. This is harder to 
say about Subject 21, a four-year-old girl who evidenced misperception on all but the 
4IAX task, which she received first following adequate training on some neutral con- 
trasts. The cases of correct phoneme production show no interesting variations be- 
cause there is no misperception evident on any of the tests. 
C O N C L U D I N G R E M A R K S 
P h o n e m e - A I I o p h o n e Relat ionships 
If the several tests used here do not produce different perceptual results, as the 
data seem to indicate, then perhaps the adult target form and the child's form are 
464 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
X < 
< 
< 
t- 
o 
c~ 
c~ 
o 
o 
-o 
o 
'-o 
.< 
o o o ~ - o o I o o o o I I o 
I I I I I - ° ~ I o o I ~ - 
LOCKE: Inference of Speech Perception, Part II 465 
typically not in a phoneme-allophone relationship. To the extent that ABX and 4IAX 
tests removed phonemic category as the basis for discrimination judgments, the over- 
all result did not change. Whether this is a general phenomenon or is specific to 
certain phonetic contrasts (for example, f-0) or subject characteristics remains to be 
established in future studies. 
Individual Differences 
Our research indicates that the normally hearing child perceives differentially the 
sounds he produces distinctively and may or may not evidence discrimination of the 
sounds he collapses in production. This inspired our earlier comment that children 
are not imperceptive, but contrasts may be misperceived. Yet, how are we to account 
for one substituting child failing to discriminate his error contrast and a different but 
outwardly similar child discriminating the same contrast, though also substituted by 
him? Are there two sources of error, one child erring for perceptual reasons, the 
other for any of a variety of nonperceptual reasons? Are the children at different 
stages in the acquisition process? I f so, has the correct discriminator come out of a 
previous period of misperception, heading now toward differential production as 
well? Or, on the other hand, is he due to acquire misperception of the sounds 
equated in production? Would spectrographic analysis of the correct discriminator's 
speech p r o d u c t i o n s show that his subst i tu t ions were il lusory, with subtle 
differences--imperceptible to the adult listener--between his co r r ec t / f / and his sub- 
stitutions of [f] for/t3/? Do correct and incorrect discriminators differ in the area of 
their phoneme boundaries, the cognitive processes by which they decide perceptual 
questions, or the sensitivity of their substitution to syllabic position and phonetic en- 
vironment? I f there were a general age trend, as there was for the/f/-/0/contrasts, 
one would still need to explain the data from three- and six-year-olds who equally fail 
to discriminate the sounds of their production collapse. 
The Basis of Phonological Structure 
The data reported in this paper are pertinent to the acquisition process, and some 
of these connections are discussed elsewhere (Locke, 1979a, 1979b, in press, a, b). In 
general, however, it appears that a simple model of the acquisition process cannot be 
right if it assumes either correct or incorrect perception on the part of children with 
nonadult speech forms. Many children have both, a linguistic fact that must be ex- 
plained by acquisition theory. Smith's reformulations (1979) of his earlier model 
(1973) are sensitive to this fact, as are Macken's. 2 But there still are the children, the 
majority of those seen in this study, who provide no evidence o f misperception. 
While referring to their problems as "phonological" may be proper in a formal 
sense--language being divisible into syntax, semantics, and phonology-- i t is not evi- 
dent that these children incorrectly understand the organization of phonology, as has 
been argued elsewhere (Ingrain, 1976). Children's deformed utterances are phonet- 
ically structured, to be sure, but the basis for such patterning might as well lie at the 
motor level as in their mentalistic concepts of linguistic organization, since each can 
produce "ruliness" at the phonetic surface. Lacking evidence of misperception, and 
without other kinds of evidence (for example, "phonetic" spelling errors), speech 
output becomes the child's only way of expressing the presumed phonological disor- 
ganization. In the absence of independent confirmation, the child's phonological dis- 
2M. A. Macken, personal communication (1978). 
466 JOURNAL OF SPEECH AND HEARING DISORDERS XLV 445-468 November 1980 
organization tautalogically becomes both the reason for his speech pattern and the 
speech pat tern itself. 
Puzzles 
One of the arguments for the organizational (or against the articulatory) nature of 
children's phonological problems has been the "puzzle," the phenomenon whereby 
children say a sound only as a substitute for another sound (Smith, 1973; Macken, 
see footnote). Puzzles have been popular because they imply that the child's articulat- 
ory abilities are sufficient to produce the missing sound, and therefore, that the 
speech disorder must be nonarticulatory. Our perceptual data suggest another in- 
terpretat ion for puzzles. We found that a child may misperceive one substituted con- 
trast and may correctly perceive another substituted contrast. Conceivably, therefore, 
a child's puggle for puddle is for perceptual reasons, his puddle for puzzle for articula- 
tory reasons. That is, the child could be trying to say puggle. Behavioral evidence is 
needed on this point, though we have one case we can present here. Jenny, age four, 
said f/0 and 0/s. She was given an AX test and a 4IAX test on each of these contrasts. 
Her errors were as follows (X-X items are the eight "sames"): 
f-O s-O x-x 
AX test 4 0 0 
4IAX test 6 2 - - 
Jenny missed all four of the f-0 contrasts on the AX test and none of the four s-0 
contrasts. On the 4IAX test, she missed six of the eight f-0 contrasts and two of the 
eight s-0 contrasts. Though we obtained no independent measure o f motor skill and 
cannot therefore argue that Jenny's [0] f o r / s / w a s for articulatory reasons, it seems 
that her er ror was not being maintained by an inability to discriminate. This would be 
harder to say of her If] f o r / 0 / b e c a u s e she consistently misdiscriminated the/f /- /0/ 
contrast. With this sort of perceptual evidence and with parallel investigation o f ar- 
ticulatory movement capabilities, puzzles may ultimately be puzzling only when in- 
quiry is restricted to the child's distribution o f surface forms. 
Misperception as Etiology: The Idiom and the Platypus 
When one encounters a child who consistently substitutes one sound for another 
but uniformly discriminates them correctly, one is inclined to think of the product ion 
problem as nonperceptual in etiology. There are several reasons why such a strictly 
drawn conclusion might not be correct. First, chi ldren have been observed to pro- 
duce what are te rmed "regressive phonological idioms," isolated forms that do not 
come up to the child's overall level of phonological progress (Ferguson and Farwell, 
1975). I f child product ion "disagrees with itself," why would one insist, unreasonably, 
that it coincide perfectly with perception? Second, if we assume that articulatory 
strategy cannot commence until different perceptual targets have beenestablished, 
there would be a built-in lag between the acquisition of correct perception and the 
emergence o f correct product ion (which, o f course, seems to be developmentally typ- 
ical). Further , however, once product ion capability developed, it still might require 
some time to diffuse th rough the lexicon (Wang, 1969; Hsieh, 1972) to the words 
used in the assessment procedure. A demonstrat ion that the child had perfect per- 
ception, then, would not prove that the child's product ion disorder was originally 
nonperceptual . The most one could safely conclude is that whatever the origins of 
the child's error, it is not presently being maintained by phonetic imperception. As 
Wang (1969) once commented, "we cannot prove that the platypus does not lay eggs 
with photographs showing a platypus not laying eggs." 
LOCKE: Inference of Speech Perception, Part II 467 
A C K N O W L E D G M E N T 
The writing of this report was supported, in part, by grant 31965-01 from the National Insti- 
tute of Mental Health~ The author is indebted to Peggy Reuler, Jeff Goldstein, and Kathryn 
Scott for assistance in testing, and to Fred Weiner and Marcy Macken for their comments on the 
manuscript. Correspondence should be addressed to the author at the Department of Hearing 
and Speech Sciences, University of Maryland, College Park, Maryland 20742. 
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