Auditory and linguistic processing

Perception & Psychophysics
1974, Vol. 16 (3), 513-521

Auditory and linguistic processing of cues
for place of articulation by infants*

PETER D. EIMAS
W. S. Hunter Laboratory ofPsychology, Brown University, Providence, Rhode Island 02912

Two- and. 3-mo~th~0Id infants ~ere found to discriminate the acoustic cues for the phonetic feature of
place of articulation III a categorical manner; that is, evidence for the discriminability of two synthetic
sp~ech patter~s ~as. pre~~nt only when the stimuli signaled a change in the phonetic feature of place. No
evidence of discriminability was found when two stimuli, separated by the same acoustic difference,
signaled acoustic variations of the same phonetic feature. Discrimination of the same acoustic cues in a
nonspeech context was found, in contrast, to be noncategorical or continuous. The results were discussed
in terms of infants' ability to process acoustic events in either an auditory or a linguistic mode.

A major conclusion of the research on the 1972) and, to a considerably lesser extent, with vowel
perception of speech over the past two decades is that stimuli under some conditions (Pisoni, 1973; Stevens,
human listeners perceive speech quite differently from Liberman, Studdert-Kennedy, & Ohman, 1969;
the way in which they perceive nonspeech sounds. Fujisaki & Kawashima, 1969).
Speech perception is said to occur in a linguistic or Although these findings are of considerable
speech mode as opposed to an auditory mode (Eimas, importance in and of themselves, they are particularly
in press; Liberman, Cooper, Shankweiler, & revealing when the discriminability functions for the
Studdert-Kennedy, 1967; Liberman, 1970; Studdert- synthetic speech stimuli are compared with the
Kennedy, 1974). Evidence for this conclusion comes discriminability functions for the same acoustic
from studies in which listeners identified and dimensions when presented in a nonspeech context.
discriminated series of synthetic speech sounds that Mattingly et al (1971) showed that the discontinuities
varied continuously along a single acoustic dimension. in the discriminability functions, so apparent when
Listeners were typically quite consistent in assigning the synthetic sounds were perceived as speech, were
phonetic labels to the various stimuli. Moreover, and absent when the stimuli were not perceived as speech.
most importantly, the ability to discriminate pairs of More specifically, they showed that variations in the
stimuli was strongly determined by the phonetic starting frequency and direction of the second-
assignments. Thus, two stimuli that were acoustic formant transition (which are sufficient for the
variations of the same phonetic category or feature perceived distinctions among the voiced stop
were discriminated only slightly better than would be consonants [b, d , g) and their voiceless counterparts
expected by chance, whereas two stimuli that were [po t, k)) were perceived categorically and continuously
separated by the same acoustic difference but in speech and nonspeech contexts, respectively. The
members of different phonetic categories were highly latter condition was arranged by presenting only the
discriminable. This form of perception has been second-formant transitions which are heard as
termed categorical and is particularly apparent for bird-like chirps. Similar effects have also been
those acoustic dimensions that distinguish the stop obtained by Miyawaki et al (1972). In addition,
consonants (Liberman, 1957; Liberman, Harris, Eimas, Cooper, and Corbit (1973) have shown the
Hoffman, & Griffith, 1957; Eimas, 1963; Mattingly, acoustic information signaling the onset of voicing is
Liberman, Syrdal, & Halwes, 1971; Lisker & perceived differently when presented in a speech as
Abramson, 1970; Abramson & Lisker, 1970; Pisoni, opposed to a nonspeech context.
1973). Categorical-like perception has also been Although it is certainly the case that all sounds,
found with other consonantal distinctions (e.g., speech or nonspeech, must undergo some common
Miyawaki, Liberman, Fujimura, Strange, & Jenkins, auditory analysis, the sounds of speech would appear
to undergo some additional, specialized processing
*The studies reported here were supported by Grant HD 05331
that permits the extraction of distinctive phonetic
from the National Institute of Child Health and Human features. It is the process of feature extraction that is
Development. United States Public Health Service. I wish to thank categorical in that it reduces the continuous variation
Jane Carlstrom. Jean Fechheimer, and Sheila Polofsky for their in acoustic-auditory information to a set of discrete
capable assistance in the collection and analysis of the data. I also feature values. The actual phonetic experience, that
wish to acknowledge my indebtedness to Franklin S. Cooper for his
generosity in making the facilities of the Haskins Laboratories is, the perception of a particular phone involves
available for the preparation of stimulus materials. additional higher processes, including most likely

513

514 EIMAS

matching a set of features with its appropriate label. speech sounds that varied in the starting frequency
Add itional evidence favoring a special speech and direction of the second- and third-formant
processor comes from studies of dichotic listening. A transitions. These variations correspond to the
number of researchers have shown that speech signals variations in articulatory movements necessary for the
are better perceived by the left hemisphere (right ear) production of bilabial stops [b, p] as opposed to apical
whereas nonspeech signals are better processed by the [d, t] or velar [g, k] stops. Discrimination of a
right hemisphere (left ear) (Kimura, 1961, 1964; particular acoustic difference was measured under
Studdert-Kennedy &, Shankweiler, 1970). Electro- two conditions: (1) when the acoustic variation
physiological studies of neural activity have also, signifies a change in place of articulation as measured
supported this conclusion in adults (Wood, Goff, & by adult identification functions, and (2) when the
Day, 1971). J variation represents acoustic variants of the same
Of particular interest have been the recent place of articulation. Evidence of greater discrimin-
electrophysiological (Molfese, 1972) and behavioral ability in the first condition permits the inference that
findings (Eimas, Siqueland , Jusczyk , & Vigorito, infants are capable of perceiving information related
1971) that the specialized speech processes may be to place distinctions in a categorical fashion and
operative as early as the first few weeks of life. Eimas hence in a linguistically relevant manner.
et al (1971) investigated the infant's ability to
discriminate small differences in voice onset time. Method
Voice onset time, which is defined by Lisker and
Procedure. The procedure was a modification of the methodology
Abramson (1964) in articulatory terms as the time developed by Siqueland and DeLucia (1969). Each infant was tested
between the release burst and the onset of laryngeal individually in a small sound-shielded room. moderately
pulsing or voicing, is a sufficient cue for illuminated by the rear-projected image of a colorful object. The
distinguishing between the voiced and voiceless stop visual image, in addition to providing illumination, tended to
consonants [b] vs [p], [d] vs [t], and [g] vs [k]. They maintain the infant's orientation to the speaker, which was situated
just above the screen, about 45 em from the infant's head. The
found that infants 1 and 4 months of age were better infant was placed in a reclining seat and presented with a blind
able to discriminate a 20-msec difference in voice nipple. The nipple was held gently by one of the Es , who listened to
onset time when the two stimuli to be discriminated music over a set of headphones. The second E monitored the
were from different adult phonetic categories, [b] and recording apparatus and controlled the presentation of the speech
patterns'. During the first 2 or 3 min, the high-amplitude criterion
[p], than when they were from the same adult and the baseline rate of high-amplitude sucking were established.
phonetic category, [b] or [pl. As was true for adult The amplitude criterion was defined as the level which yielded a
listeners (Abramson & Lisker, 1970), acoustic baseline sucking rate of approximately 20 or 30 responses/min. By
variations of the same phonetic feature were not permitting the amplitude criterion to vary from infant to infant, it
discriminable. In later studies, Eimas (in press) was was possible to reduce the variability associated with baseline rates
of sucking as well as to establish a baseline rate for each infant such
able to replicate these results with the apical stops, that changes in either direction could occur without serious
[d, t], and to find some evidence for the categorical contamination by either floor or ceiling effects. Immediately after
perception by young infants of a voicing distinction obtaining the baseline rate, the first speech sound was made
not found in English. contingent upon high-amplitude sucking. If the time between each
high-amplitude sucking response was at least t sec, then each s'tich
Additional research has shown that infants between response produced one presentation of the stimulus pattern
the ages of 2 and 6 months are sensitive to differences 300 msec in duration plus 700 msec of silence. However, if the
in place of articulation, acoustically represented by infant produced a burst of sucking responses with interresponse
variations in the second- and third-formant times less than I sec, as was typical, then each response did not
transitions (Moffitt. 1971; Morse, 1972). Although produce one presentation of the stimulus. Rather, each response
recycled the timing apparatus and the I-sec on period began again.
Morse has contended that infants process place This limitation in the presentation of auditory feedback was
distinctions in a linguistically relevant manner, the imposed to prevent the occurrence of the reinforcing sound longer
supporting evidence was not compelling. It is toward a than t sec after the last response.
resolution of this issue, that is, the manner in which The presentation of an auditory stimulus in this manner typically
results in an increase in the infant's rate of high-amplitude sucking,
place information is perceived by infants, that the compared with the baseline rate. After several minutes of this
present studies were directed. Another purpose was to contingency (the time varies from infant to infant from about 4 or
determine whether the mechanisms that are necessary 5 min to over 15 min), the infant usually shows a decrement in
to decode information signaling place of articulation performance, presumably as a result of a diminution in the
are, as is apparently the case with adult listeners, the reinforcing quality of the once novel speech stimulus. When the rate
of sucking diminished by 20% or more for 2 consecutive minutes
unique property of the speech processor. compared with the minute immediately preceding the first minute
of decrement, the feedback stimulus was changed without
EXPERIMENT I interruption by switching the channel selector on the tape deck. The
second synthetic speech pattern was presented, likewise contingent
upon high-amplitude sucking, for 4 min, after which the testing
The purpose of Experiment I was to determine session was terminated.
whether the perception of place distinctions by young One group of infants, Group D, received two stimuli, one of
infants was categorical. The stimuli were synthetic which signaled the adult phonetic category [d] and the other the

ACOUSTIC CUES FOR PLACE OF ARTICULATION IN INFANTS 515

phonetic category [g]. The second group of infants, Group S, Table 1
likewise received two stimuli, but these sound patterns were Starting Frequencies (in Hz) of the Second- and
acoustic variations of the same adult phonetic category [dl. The Third-Formant Transitions: Experiment
order in which the two stimuli were presented was counterbalanced Stimulus 1 Stimulus 2 Difference
across infants in both groups. The infants in the control condition,
Group C, were randomly assigned one of the four stimuli F-2 1845 1996 151
administered to Groups D and S. At the point at which a change in Group D 337
F-3 2862 2525
stimulation would have occurred for the infants of Groups Sand D, F-2 1541 1695 154
the records of the control infants were marked, the channel selector Group S
F-3 2862 3195 333
control was switched, and the session continued for 4 min. Thus,
the control records were completely comparable with those of the Note-Adult listeners consistently identified th e stimuli for
experimental infants. Given that infants are highly responsive to Group S and Stimulus 1 for Group D as [d], Stimulus 2 for
novel stimuli, the presentation of a new, discriminable stimulus Group D was identified as f sl.
would be expected to result in a different rate of sucking when
compared with the sucking rates for infants who did not receive a
Intensity readings were made with a General Radio Type 155l-C
change in stimulation. Thus, either an increase in response rate
sound-level meter, B scale. The background noise was produced
associated with a change in stimulation greater than that shown by
almost entirely by the room exhaust system and the slide projector
the control infants or a decrease less than that of the controls is
fan.
taken as inferential evidence that the infants perceived the two
Subjects. The Ss were 24 2-month-old and 24 3-month-old
stimuli as different,
infants from the Greater Providence, Rhode Island, area. Half of
Stimuli. The stimuli were four synthetic speech sounds prepared
the infants at each age level were males and females. In order to
by means of the parallel resonance synthesizere at the Haskins
obtain complete data on 48 infants, it was necessary to test 115
Laboratories by Pisoni (1971). Each stimulus was 300 msec in
infants. The success rate of approximately 40% is typical of the
duration, with the initial 40 msec simulating a period of closure
satiation/release-from-satiation procedure that we have used to
voicing by means of a low-amplitude first formant centered at
assess the speech processing capacities of young infants. There were
150 Hz. The next 40 msec was a period of transition during which
no reliable differences in failures due to experimental condition,
all three formants moved from their starting frequencies to their
age, or sex. The reasons for failure to complete testing were many
terminal steady-state values of 743, 1,620, and 2,862 Hz for the
and included such factors as falling asleep (33%), crying (25%),
first. second, and third formant, respectively. These steady-state
initial failure to suck on the nipple (20%), ceasing to suck during
formant values are appropriate for the American English vowel
the course of the experiment (7%), and a group of factors consisting
[ae]. The steady-state portion of each pattern was 220 msec in
offailure to show satiation, an extremely erratic pattern of sucking,
duration. The starting values for the second- and third-formants
equipment failure, and E error (15%). The majority of the infants
are given in Table I for each ofthe two stimuli presented to Groups
(78%) who failed to complete the session were eliminated prior to
D and S. along with their phonetic identification as determined by
the shift in stimulation. There were no reliable differences in the
adult listeners (Pisoni, 1973). All four stimuli had the same
infants who were eliminated after the shift as a function of sex or
first-formant starting values, ISO Hz. As may be seen in Table I.
experimental treatment, and 80% of these infants were eliminated
the only differences among the stimuli were in starting frequencies
for crying or falling asleep. The criterion for the former was loud
and direction of the second- and third-formant transitions (and, of
crying and a failure to take the nipple. whereas the criterion for the
course, in one instance. in the phonetic identification or place of
latter was the characteristic sucking pattern associated with sleep.
articulation value). Of importance to note is the fact that the
that is. brief bursts of very low-amplitude sucking. Most of the
acoustic differences between the two stimuli used for Group D were
postshift eliminations occurred during the first or second postshift
very nearly identical to the differences between the stimuli used for
minute.
Group S. Thus. any differences in discriminability between the two
As often as possible, the infants were assigned randomly to the
groups cannot be attributed to an inequality in the acoustic
three conditions. However, given the high attrition rate and the
differences between the stimuli. For additional details concerning
restrictions that the three groups (each with 16 infants) be
the construction of these stimuli, the reader is referred to Pisoni
counterbalanced with respect to age. sex, and order of stimulus
(1971).
, presentation. random assignments could not always be made.
The stimuli were recorded on high-quality magnetic tape from
which continuous loops were made, with each 300-msec speech
pattern separated by 700 msec of silence. There were several copies
of each tape loop. The loops used for Groups D and S had one
Results and Discussion
stimulus on Channel I and the second stimulus on Channel 2. The The mean number of sucking responses is displayed
control tapes contained the same stimulus on both channels. This in Fig. 1 as a function of minutes and treatments. An
arrangement of the stimuli permitted all infants to be treated in a analysis of the minute-by-minute sucking rates for the
like manner as well as the nearly instantaneous switching between 5 min immediately prior to the shift in stimulation (or
stimuli.
Apparatus. Part of the apparatus was a blind nipple on which the at that point in time when a shift would have occurred
infant sucked. The positive pressure generated by the infant's in the case of the control infants) revealed nonreliable
sucking was transduced to provide a record of all sucking responses differences between groups. As would be expected
as well as a digital record of criterional high-amplitude sucking from the nature ofthe experiment, the mean response
responses by means of a HP 7202B polygraph and a Hunter digital
timer. Additional equipment included a two-channel tape deck
rate for the 2 min before shift (the satiation period)
(Sony Model TC 850), a VM Model 33-1 speaker, power supply, was significantly lower than the third minute before
HP 8805A preamplifier, and Lafayette 5710 event timer, arranged stimulus change (p .01). <
to provide auditory feedback when the power supply was activated Inasmuch as the measure of discriminability is
by a criterion response. Each sucking response of criterion based on a change in response rate correlated with a
amplitude activated a power supply for 1 sec (or restarted a period
of l-sec activation), which resulted in a rapid increase in the change in stimulation, and given that there were
intensity of auditory feedback stimulation from an inaudible level to individual differences in response rates during the
one about 13 to 15 dB above the background noise level of 63 dB. satiation period, the analyses of postshift performance

516 EIMAS

75 I
GROUP 0 GROUP S GROUP C
I I
'"
w I I
'"
z
0
I I
~
60
I I
'"
......
0'; I I
I Fig. 1. Mean number of sucking responses
o I as a function of time and experimental
Z I I conditions. Time is measured with reference
/"
45
:>2
V
:> ,...../,.
I I
I
to the moment of stimulus shift, which is
indicated by the dashed line. The baseline rate
'"
0
u, , I of sucking is indicated by the letter"B."
I
:~
CIt 30
w
OIl I

..L L. L. .! -l. . L- LJ. 1.- .L~
~
:::>
• I • I
Z I I
Z
-<I:
15
I I
w
I I
~
I I
-i_L..L-Lfu-L_L.J '. I I, I

8 5 " 3 2 11 1 2 3 4 S 5 4 " 2 I 1 234 S 5 4 1 1 3

TiME (min)

were conducted on difference scores. For each infant, are presented in a speech context, as in Experiment I,
the mean response rate for the 2 min immediately and when they are presented in a non speech context.
preceding the stimulus shift was subtracted from each The speech stimuli for this experiment were
of the four l-rnin measures of postshift performance. two-formant synthetic speech patterns, which varied
An analysis of variance, Groups by Minutes, in the starting frequency and direction of the
performed on these difference scores, revealed a second-formant transition only. AU other characteris-
significant groups effect, F(2,45) = 4.5, p < .025, tics of the stimuli did not vary from one pattern to
and a significant Groups by Minutes interaction, another. Variations in the second-formant transition
F(6,135) = 8.4, p < .001. Group D, which showed a are by themselves sufficient cues to signal variations in
mean increment of 4.1 responses/min for the 4-min place of articulation, and indeed, as Liberman et al
postshift period, differed reliably from Groups Sand (1967) have noted: " ... [the second-formant
C (p < .025 in each instance). Groups Sand C, which transition] is probably the single most important
showed mean decrements of 6.1 and 4.8 carrier of linguistic information in the speech signal
responses/min, respectively, did not differ signif- [p, 434]." Based on identification functions from
icantly. The significant interaction, as can be seen in adult listeners obtained by Mattingly et al (1971),
Fig. 1, was primarily a function of the increase in rate pairs of synthetic speech patterns, separated by a
of responding shown by Group D over the 4-min constant acoustic difference, were selected such that
postshift period, whereas Groups Sand C tended to the two stimuli were perceived either as different
show a decreasing rate of response with time.! phones, [b] and [d], or as the same phone, [b]. The
The cues for place of articulation, like the cues for two different types of stimulus pairs corresponded to
voice onset time, are discriminated in a the Group D and Group S stimuli of Experiment 1.
categorical-like manner by young infants; that is to In order to present the identical relevant acoustic
say, the infant's ability to discriminate place cues is information in a non speech context, additional
determined largely by whether or not the acoustic patterns were synthesized that eliminated all acoustic
stimuli signal the same or different values along the features, except the second-formant transitions of the
phonetic feature, place of articulation. Before speech stimuli. These patterns, 40 msec in duration,
considering the perceptual mechanisms that might be are perceived as bird-like chirps by adult listeners
responsible for processing of speech in a linguistic (Mattinglyet aI, 1971). Thus, both sets of stimuli vary
mode, we wish to consider whether these mechanisms in precisely the same manner, but yet are perceived in
are part of the more general auditory processing radically different ways by adult listeners.
system or whether they are part of the specialized Should both sets ofstimuli be perceived in the same
speech processor. categorical manner, then it is possible to conclude
that, at least during infancy, the more general
EXPERIMENT II auditory processing system is differentially sensitive to
variations in rapidly changing frequency values.
Experiment II compared the infant's ability to Furthermore, it would seem that the points of greater
discriminate acoustic cues for place when these cues discriminability were selected to mark phonetic


boundaries (ct. Stevens, 1972; Stevens et ai, 1969). Table 2
However, should categorical-like perception be Starting Frequencies (in Hz) of the Second-Formant
Transitions: Experiment II
characteristic of only the speech stimuli (as in adult
listeners), then categorical decisions regarding Stimulus Diffe-
phonetic feature values cannot be ascribed to the 1 2 renee
fu nctioning of the general auditory processing system, Pair 1 F-2 1312 1541 229
Group 0
but rather must be considered to be a result of some Pair 2 F-2 1386 1620 234
form of additional linguistic processing to which only Group S F-2 1232 1465 233
the sounds of speech are subjected. Note-Adult listeners consistently identified the stimuli for
Group S and Stimulus 1 for both Group D pairs as [b],
Method Stimulus 2 for both Group D pairs was identified as [d],
Stimuli. The speech stimuli were six synthetic speech patterns
constructed by means of a parallel resonance synthesizer at the after the stimulus change did not differ reliably due to sex or
Haskins Laboratories by Mattingly et al (1971). Each stimulus was experimental treatment and most of the infants were eliminated
245 msec in duration. The initial 15 msec simulated closure voicing before the third postshift minute. When possible, infants were
by means of a low-amplitude first formant at 150 Hz. The following randomly assigned to the six conditions. But, again, the high
40 msec was a transitional period, during which the first and attrition rate and the restrictions that the six groups be balanced as
second formants moved from their starting values to their terminal closely as possible for age, sex, order of stimulus presentation, and,
steady-state values of 743 and 1,620 Hz, respectively. The in the case of the infants in Group D. for stimulus pair, completely
steady-state portions were 190 msee in duration. These stimuli were random assignments were simply not possible.
perceived as the voiced stops [b] or [d] plus the vowel [ae], The
nonspeech stimuli, 40 msec in duration, were likewise synthesized Results and Discussion
by means of the parallel resonance synthesizer. Each non speech
pattern corresponded exactly to one of the second-formant
An analysis of the response rates for the 5 min
transitions of the speech stimuli. Table 2 gives the starting immediately preceding the stimulus change revealed
frequencies for the six second-formant transitions. The difference no reliable differences due to experimental conditions
in the second-formant starting frequency between the two stimuli of or type of stimulus, speech or nonspeech. All six
the two pairs used for Group D and the single pair used for
groups showed a reliable increment in sucking rate at
Group S was approximately the same. This equality held, of course,
for both the speech and nonspeech stimuli. The stimuli were the third minute before shift compared with the
recorded and made into continuous loops, as in Experiment 1. The baseline rate (p < .01) and a reliable decrement
silent interval between successive stimuli was 755 msec for the during the final 2 min before shift, as would be
speech sounds and 960 msec for the nonspeech sounds. expected (p < .01).
Apparatus. The apparatus was the same as that used in
Experiment 1.
Difference scores were again used in all analyses of
Procedure. The general procedural details were the same as those postshift performance. The mean changes in response
used in Experiment 1. For each type of stimulus, speech or rates over the final 4 min are shown in Table 3.
nonspeech, there were three groups of 16 infants, D, S, and C. The Preliminary analyses of the postshift data revealed no
infants of Group D (both speech and non speech) received one of significant differences as a function of age, sex, order
two pairs of stimuli. half of the infants receiving one pair and the
remaining infants the other pair. When the stimuli were speech of stimulus presentation, or, in the case of the infants
sounds. one stimulus of each pair signaled the phonetic category assigned to Group D, the stimulus pair. An analysis
[bl. while the second stimulus signaled the phonetic category [d]. of variance, Type of Stimulus (speech vs nonspeech)
Two different pairs were used to be sure that. in at least one by Groups (D vs S vs C) by Minutes yielded only one
instance, the two stimuli lay on opposite sides of the phonetic
boundary. The infants in Group S received a single pair of stimuli,
significant effect, namely, the Groups by Type of
which, when speech sounds, were both representatives of the Stimulus interaction, F(2,90) 4.1, P < .025).
category [b]. The control infants (Group C) received one of the six Individual comparisons revealed the following:
speech or six non speech stimuli, randomly selected. All stimuli were (l) When the stimuli were synthetic speech patterns,
presented at approximately 15 dB above a background noise level there was evidence for categorical perception in that
of63 dB (B scale, Type 1551-C General Radio sound-level meter).
Subjects. The Ss were 96 infants from the Greater Providence, Group D responded at a reliably higher rate than did
Rhode Island, area. Approximately half of the infants were males Groups Sand C, which did not differ from each other.
and half females. Likewise, approximately half of the sample were 2 (2) When the stimuli where nonspeech sounds, there
months of age and the remaining infants were 3 months old.
Forty-four percent of the infants tested completed the experiment,
and there were no reliable differences in the rate of failure due to Table 3
age, sex, type of stimulus, or experimental treatment. Of the 122 Mean Recovery in Response Rate (Responses Per Minute) for
infants who failed to complete the experiment, 34% cried, 27% fell the Entire 4-Min Postshift Period: Experiment II
asleep. 12% failed to suck on the nipple at all. 80/0 stopped sucking Experimental Condition
at some time during the course of the experiment, and 18% were Group 0 Group S Group C
Stimuli
eliminated for a variety of reasons. including failure to achieve the
satiation criterion, very erratic responding, and equipment failure. Speech +8.5 -4.6 -1.2
The majority (86%) of the infants who failed to complete the Nonspeech +4.0* +7.9 +.6
experiment were eliminated before the stimulus change. and of
those who were eliminated after the change, 83% either fell asleep "In a replication study with nine infants, the mean increment
or cried. As in the first experiment, the infants who were eliminated in response rate was +7.3 responses/min.

518 EIMAS

was no evidence for categorical perception; Groups D discriminable in one context (nonspeech) might not be
and S did not differ reliably. (3) Although Group S did discriminable in another context (speech), and
differ from Group C, the infants of Group D did not (3) what functions perception in a speech mode might
differ significantly from the control infants when the serve in the infant during the earliest stages of
stimuli were non speech sounds. language acquisition. .
It is, of course, possible that the auditory The major theoretical positions pertaining to the
processing system finds some pairs of nonspeech perception of speech are complex models, in that
sounds more discriminable than other pairs (cf, perception is assumed to be more directly linked to
Mattingly et al, 1971). On the other hand, it is internal mediating events than to external acoustic
likewise possible that the slightly depressed events or their immediate auditory transforms (see,
performance of the nonspeech Group D (compared for example, Liberman, 1957, 1970; Liberman et ai,
with Group S) was due to sampling error. Indeed, the 1967; Stevens & House, 1972). Thus, in the motor
difference between thq two groups could be attributed theory of speech perception of Liberman and his
to the relatively poor performance of only four infants associates, decoding of the incoming acoustic signal is
in Group D. To test these alternatives, an additional made by reference to invariant motoric commands to
nine infants were tested on their ability to the articulatory system, undoubtedly at the level of
discriminate the two pairs of nonspeech chirps neural activity. Exactly how the acoustic information
previously used for Group D. The results indicate that makes contact with these central articulatory
these stimuli can be reliably discriminated and that commands has not as yet been fully explicated. In a
the original estimate of discriminability may well have similar manner, the analysis-by-synthesis model of
been underestimated due to sampling error: the mean Stevens and his colleagues makes the assumption that
increase in response rate was 7.3 responses (p < .05), perception occurs when the temporarily stored speech
very near the performance level of Group S. event, in auditory form, is matched by a second,
Regardless of the true level of discriminability for internally generated or synthesized representation of
the stimuli of the nonspeech Group D, it is the case the speech event in question. This process of
that infants discriminate variations in the generation must necessarily involve considerable
second-formant transition quite differently when they knowledge of production processes, more specifically,
are presented in a speech context as opposed to a of the rules by which distinctive phonetic features are
nonspeech context. Further confirmation of this converted into articulatory commands and of the rules
conclusion comes from comparisons of Groups D and by which auditory patterns are associated with these
S, which received speech stimuli, with the same . commands.
groups which received nonspeech stimuli. A 2 by 2 Although motor theories of speech perception are
analysis of variance revealed a highly significant possible models of adult speech perception, the
Groups by Type of Stimulus interaction, FO,60) = application of this class of model to the
20.5, P < .001: Group S, which received speech speech-processing capacities of the infant raises
stimuli, responded less frequently than did the certain difficulties. Most prominent of these is the
remaining three groups, which, in turn, did not differ need to explain how the young, virtually inarticulate
significantly from one another. infant has come to possess the complex knowledge
In summary, the results of these two experiments required for the conversion of phonetic features to
indicate that infants are capable of categorizing articulatory commands, and how he has come to
continuous variations in the acoustic dimension that associate particular auditory patterns with articula-
signal adult phonetic distinctions corresponding to tory commands. Without ascribing this knowledge to
place of articulation. Moreover, the manner in which the biological endowment of the infant, there would
this categorization takes place agrees perfectly with appear to be no way in which an infant could have
the three major and possibly universal phonetic acquired this information by traditional means during
distinctions based on place of articulation." Finally, the first few weeks or months of life. However, to
the processing system that subserves perception of the attribute this knowledge to the infant's biological
phonetic feature of place differs from the system that endowment would seem to extend considerably the
is capable of processing the same acoustic information cognitive competencies that we are willing to impute
in a nonspeech context. to genetically determined factors.
A number of researchers have begun to consider
GENERAL DISCUSSION alternate models of speech perception that are based
on feature detectors and that do not require
It remains now to consider 0) the perceptual knowledge of production routines (Abbs & Sussman,
mechanisms that could be responsible for the 1971; Cole & Scott, 1972; Cooper, in press; Eimas &
categorical perception of place cues in speech Corbit. 1973; Eimas, Cooper. & Corbit, 1973;
contexts, (2) how acoustic differences that are Lieberman, 1970; Stevens. 1972, 1973).3 Although


feature detectors which permit phonetic decisions which is more closely tied to physical (acoustic)
could be either auditory or linguistic in nature, the differences per se than is that of the speech analyzers.
weight of evidence favors linguistic feature detectors (For evidence pertaining to the insensitivity of the
(but see Stevens, 1973, for an account of place speech processor to variations in the acoustic
discrimination based on auditory property detectors). difference between two phonetically distinct sounds,
Recently, Eimas and Corbit (1973) and Eimas, the reader is referred to Eimas, in press.) In essence,
Cooper, and Corbit (1973) have presented evidence then, .we have tried to argue that the discriminability
consistent with the hypothesis that there exist of speech in infants is based primarily on the detection
phonetic feature detectors for the acoustic of different values of one or more phonetic features,
consequences of the two modes of voicing found in such as voice onset time or place of articulation. 4
English and numerous other languages (Lisker & The ability of infants (and adults) to discriminate
Abramson, 1964). These detectors were assumed to be certain variations of second-formant transitions in a
sensitive to relatively restricted ranges of complex nonspeech context and yet be unable to discriminate
acoustic energy (voice onset time), part of the central the same acoustic information when it is presented in
speech processing system, and finally the direct a speech context is a seemingly paradoxical finding.
mediators of the categorization of voicing As mentioned above, it must be the case that acoustic
information. Similarly, Cooper (in press) and Cooper events, regardless of their nature, initially undergo a
and Blumstein (1974) have found evidence for the considerable degree of common auditory analysis, but
existence of phonetic feature detectors underlying the as the results indicate, some of the auditory
perception of the acoustic consequences of the three information from this common processing. is
major place distinctions. If these phonetic feature apparently lost or not available when the stimuli are
detectors exist and are operative early in the lives of speech signals. Perhaps the information arising from
infants, then it is possible to accommodate the the additional linguistic analysis that only the sounds
categorical perception of infants without recourse to of speech undergo takes precedence in some manner
motoric theories of speech perception (Eimas, in over the output information of the auditory analyzers.
press; Cutting & Eimas, in press). Essentially, it has Of equal likelihood, however, is the hypothesis that
been argued that, given the passive nature of a feature linguistic processing reduces the amount of auditory
detector system of analysis, the presentation of an information that can be held in a temporary, probably
acoustic signal with sufficient linguistic information preperceptual store (cf, Massaro, 1972), as a con-
to activate the speech processor (cf. Molfese, 1972) sequence of the additional time and/or processing
will likewise activate those phonetic feature detectors capacity required by the linguistic analysis. Thus,
for which there is an adequate stimulus. Continued after linguistic processing, the relatively brief, but
presentation of the same speech sound eventuates in complex, auditory information associated with
the adaptation of the stimulated detectors. This phonetic features becomes unavailable, for all intents
adaptation may be related to the diminution of the and purposes, to response decision units. Although at
reinforcing properties of novel speech stimuli as they this time the available evidence does not permit a
become increasingly familiar and the subsequent resolution ofthis problem, it is of interest to note that
reduction in effort to obtain the stimulus. The a number of researchers have considered the
introduction of an acoustically different, but categorical nature of speech perception to be due, at
phonetically identical, speech pattern will not be least in part, to memorial processes that affect the
experienced as novel by the infant, whereas an stored auditory analogs of the acoustic input (cf.
acoustically and phonetically different speech sound Fujisak i & Kawashima, 1969; Pisoni, 1973).
will be perceived as novel. From a phonetic feature The capacity of infants to perceive speech in a
analysis and the infant's strong attraction to novelty, linguistic mode through the activation of a special
it is easily predicted that the postshift period of speech processor with phonetic feature detectors
Group D should be marked by a substantial serves a number of functions. In the first place, this
increment in response rate to obtain the new stimulus. form of analysis of speech provides the infant with an
On the other hand, the postshift period of Group S automatic means for the recognition of speech. As a
(and, of course, of Group C) should reveal a consequence, speech signals will undergo special
continued decrease in the rate of responding. As for processing, without conscious decisions on the part of
accommodating the continuous discrimination of the listener (infant or adult), provided only that there
second-formant transition variations when presented is sufficient linguistic information in the signal to
in a nonspeech context, we need only assume that activate the speech processor (cf. Eimas, Cooper, &
there was not sufficient linguistic information in the Corbit, 1973; Mattingly et aI, 1971). Secondly, the
signal to activate the -speech processor. Hence, the speech processing system, with its phonetic feature
analysis of these sounds is restricted to the auditory analyzers, not only provides information concerning
processing system, the discriminative capacity of the phonetic feature structure of the speech sounds

520 EIMAS

but also automatically acts to segment the continuous voicing of initial stops: Acoustical measurements. Word, 1964,
stream of speech into discrete elements-a necessary 20, 384-422.
step for the analysis of speech and language. Finally, LISKER, L., & ABRAMSON, A. S. The voicing dimension: Some
experiments in comparative phonetics. in Proceedings of the
this form of processing, in not requiring that the Sixth International Congress ofPhonetic Sciences. Prague, 1967.
infant actively learn to recognize speech or to segment Prague: Academia, 1970. Pp. 563-567.
it into phonetic features must certainly hasten, and MASSARO, D. W. Preperceptual images, processing time, and per-
perhaps even make possible, the acquisition of human ceptual units in auditory perception. Psychological Review, 1972,
79, 124-145.
languages.
MATTINGLY, I. G .. LIBERMAN, A. M., SYRDAL, A. K., &
HALWES, T. Discrimination in speech and nonspeech modes.
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ABBS, 1. H., & SUSSMAN. H. M. Neurophysiological feature detec- & JENKINS, J. J. Cross-language study of the perception of the
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ABRAMSON, A. S., & LISKER, L. Discriminability along with voic- Psychology, Tokyo, 1972. (Also in Status Report on Speech
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tion, Boston, Massachusetts, April 1972. adults: Auditory evoked responses to speech and noise stimuli.
COOl~ER, W. E. Adaptation of phonetic feature analyzers for place Unpublished PhD dissertation, The Pennsylvania State Univer-
of articulation. Journal of the Acoustical Society of America, sity, 1972.
in press. MORSE, P. A. The discrimination of speech and nonspeech
COOPER, W. E., & BLUMSTEIN, S. E. A "labial" feature analyzer in stimuli in early infancy. Journal of Experimental Child
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CUTTING, 1. E., & EIMAS, P. D. Phonetic feature analyzers in the sounds. Unpublished PhD dissertation, University of Michigan,
processing of speech by infants. In J. Kavanagh and J. E. 1971. (Also in Supplement to Status Report on Speech Research,
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EIMAS, P. D., SIQUELAND, E. R., JUSCZYK, P., & VIGORITO, J. perception of consonants. Paper presented at Symposium on
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LIBERMAN, A. M., HARRIS, K. S., HOFFMAN, H. S., & GRIFFITH,
B. C. The discrimination of speech sounds within and across NOTES
phoneme boundaries. Journal of Experimental Psychology,
1957, 54, 358-368. I. In one respect, the present findings differ from those obtained
LIEBERMAN, P. Towards a unitied phonetic theory. Linguistic with the dimension of voice onset time: the recovery function for
Inquiry, 1970, 1. 307-322. Group 0 showed a rising function, whereas for voice onset time, the
LISKER, L., & ABRAMSON, A. S. A cross-language study of Group 0 recovery function attained its maximum response rate


during the initial 2 min. This effect appears to be real in that the extent by the phonetic composition of the acoustic event.
same rising function for Group D was found in a replication study 3. We recognize that there exist, as yet, a number of unresolved
using similar three-formant synthetic speech stimuli. The recovery problems in hypothesizing a model of speech perception based on
function for the comparable Group D in Experiment II, showed a the extraction of phonetic information by feature detectors. These
less pronounced increment over time, with the peak response rate problems include, for example, delineating the phonetic features
occurring at the third postshift minute. The reason for the delay in and the invariant stimulus information necessary for the activation
the postshift response peak with place cues is not clear (but see of the various detectors. The latter issue is particularly difficult,
Cutting and Eimas, in press, for some possibly analogous findings given the extent to which a number of cues sufficient for signaling
in the adult speech perception literature). phonetic feature distinctions are context-conditioned, and vary
2. Comparison of the pattern of results of the first experiment greatly from speaker to speaker (d. Liberman et aI, 1967).
with that obtained by Pisani (1971, 1973) indicates that infants may Whether these issues can be resolved is to a large extent an
be bound by phonetic feature values in discriminating speech empirical problem. What we have tried to do in this paper and
signals even more than adult listeners. Pisani, using a variety of others is to demonstrate that this form of analysis can accommodate
psychophysical procedures, found that the level of discriminability at least a portion of the speech data, whether from infant or adult
for the stimuli of Group S was consistently above chance, albeit listeners.
only 7%-100/0. It will be recalled that the recovery function for 4. It should be borne in mind that the feature detector model is
Group S did not differ from that of the control infants. Moreover, used in the present paper to accommodate the discriminability data
in Experiment II, an even larger acoustic difference than used by only. It is obviously the case that additional, high-level processes of
Mattingly et al (1971) failed to produce any evidence of integration, as well as some form of matching sets of distinctive
within-phonetic category discrimination. Whether infants are features with appropriate labels, are necessary before an
actually more constrained than adult listeners by the phonetic identification response can be made.
feature structure or whether the apparent difference is one
attributable to procedural differences remains to be determined. In (Received for publication March I, 1974;
any event, there appears to be ample evidence that the revision received July 6, 1974.)
discrimination of speech signals by infants is controlled to a large

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