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R N Aslin

Publications and source records attributed to R N Aslin.

At least 37 records · Page 2Linked to original sources
PubMed1989

Discrimination of frequency transitions by human infants.

Difference limens (DLs) for linear frequency transitions using a 1.0-kHz pulsed-tone standard were obtained from 6- to 9-month-old human infants in a series of three experiments. A repeating standard "yes-no" operant headturning technique and an adaptive staircase (tracking) procedure were used to obtain difference limens from a total of 71 infants. The DLs for 300-ms upward and downward linear frequency sweeps were approximately 3%-4% when the repeating standard was an unmodulated 1.0-kHz pulsed tone of 300-ms duration. These DLs for frequency sweeps were not significantly different from DLs for frequency increments and decrements using 330-ms pulsed tones [J. M. Sinnott and R. N. Aslin, J. Acoust. Soc. Am. 78, 1986-1992 (1985)]. The DLs for frequency sweeps of 50 ms appended to the beginning or the end of a 250-ms unmodulated 1.0-kHz tone were approximately 6%-7%. This greater DL for brief frequency sweeps was confirmed by varying the duration but not the extent of the sweep. Finally, DLs were greater than 50% when the repeating standard was a 50-ms rising or falling frequency sweep appended to the beginning of a 250-ms unmodulated 1.0-kHz tone. These results suggest that rapid frequency transitions are much more difficult to discriminate from frequency transitions of the same category (rising or falling) than from either a frequency transition of the opposite category (falling or rising) or an unmodulated tone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Identification of vowels in "vowel-less" syllables by 3-year-olds.

The ability of 3-year-old children to perceive the identity of vowels in full-vowel and silent-center, consonant-vowel-consonant (CVC) syllables was investigated using a two-alternative pointing procedure. Silence replaced the middle 10%, 35%, 65%, or 90% of the steady-state formants of synthetic "bad" and "bud" syllables. Identification of the two full-vowel syllables was 87% correct, whereas performance for the silent-center syllables was somewhat lower (72%, 70%, 67%, and 66% correct for the 10%, 35%, 65%, and 90% deletion stimuli, respectively). The performance of individual children fell into two subgroups: (1) those who performed like adults by maintaining correct vowel identification for all of the silent-center syllables, and (2) those who identified the full-vowel syllables correctly but performed at chance for all of the silent-center syllables. Three additional experiments showed that none of the children performed poorly when noise replaced the gap in the silent-center syllables. These results demonstrate that many 3-year-olds can identify vowels correctly in CVC syllables in the absence of the full spectral properties of steady-state formants.

Adult↗
PubMed1988

Perceptual development.

Our selective review of perceptual development has attempted to highlight three different structural levels: sensory primitives, perceptual representations, and higher-order operations. Each of these levels appears to undergo considerable development. Moreover, both within- and between-level developments appear to influence the emergence and form of perceptual abilities. The distinction between levels is often elusive, defined more by task than by logic. As a result, some distinctions seem clearer than others. First, the emergence of sensory primitives, particularly in the visual modality, may severely constrain the quality of perceptual representations. Despite these constraints, however, there is strong support for the hypothesis that distal stimulation is primary at the level of perceptual representation. Second, perceptual representations, particularly in the domain of speech sounds, appear to undergo considerable reorganization that cannot be attributed to the emergence of sensory primitives. Although some of this development in perceptual representations can be attributed to representational changes per se, much of this reorganization at the level of perceptual representations appears to be mediated by emerging cognitive operations and linguistic processes. Unfortunately, an evaluation of reorganizational factors (e.g. familiarity) that are potentially independent of higher-order cognitive and language influences is confounded by the co-occurrence of postnatal experience with the emergence of more mature cognitive and language abilities. Obviously, to disentangle the effects of experience from the effects of higher-order processes on perceptual development, it would be necessary either to eliminate these higher-order processes or to accelerate their potential influence. Controlled experiments of this sort are difficult or impossible to conduct with humans, although suitable animal models of some aspects of perceptual development may be possible. Current and future research on perceptual development appears to be directed toward three general goals. First, the ecological and psychophysical perspectives appear headed for a marriage that will enhance both the richness and the utility of these two approaches. Second, computational techniques appear to offer a new level of sophistication that should force developmentalists to sharpen their hypotheses and to make point predictions rather than simple directional predictions. Third, the search will continue for methods to assess the role of higher-order processes.

Child↗
PubMed1987

The amplitude and angle of saccades to double-step target displacements.

Two experiments examined the magnitude and direction of the initial saccade to a target that underwent two displacements within 200 msec. When the amplitude of the two target displacements was held constant at 10 deg but the angle of the displacements differed by 45 deg, a small but significant number of intermediate-angle saccades occurred. These intermediate-angle saccades were directed to locations between the two targets, thereby generating an angle transition function, and their amplitude was 10-20% less than the amplitude on single-step displacements. These intermediate-angle saccades were not simply the result of programming an oblique saccade because amplitude transition functions virtually identical to those reported by Becker and Jürgens [Vision Res. 19, 967-983 (1979)] for horizontal saccades were obtained for double-step target displacements limited to oblique saccades. Finally, when both target amplitude and target angle were varied in double-step displacements, it became clear that the timing of the amplitude transition function and the angle transition function was not coincident. Across conditions, the angle transition function occurred at a consistent time prior to the initial saccade, whereas the amplitude transition function occurred at a variable time prior to the initial saccade. Because these amplitude and angle transition functions appeared to be dissociated, a modified model of the saccadic programming system for double-step displacements was proposed.

Eye Movements↗
PubMed1987

Binocular VEP summation in infants and adults with abnormal binocular histories.

Visual evoked potentials (VEPs) were recorded under binocular and monocular viewing conditions in 19 2- to 10-month-old infants, 19 stereodeficient adults, and 12 normal adults. VEPs were elicited by medium contrast, phase-alternated checkerboards with check sizes ranging from 10-52 min of arc. Binocular VEP summation was defined as the percentage by which the binocular VEP amplitude exceeded the mean of the two monocular VEP amplitudes. In the stereonormal adults, binocular VEP summation was significantly greater than zero and significantly less than 100%. In the stereodeficient adults, binocular VEP summation was not significantly greater than zero. These findings support the hypothesis that the magnitude of binocular VEP summation reflects the activation of binocular cortical neurons. However, binocular VEP summation in the infants averaged approximately 95%. Moreover, infants under 5 months of age, many younger than the reported age of onset for stereopsis, showed binocular VEP summation of nearly 145%. The significantly higher level of binocular VEP summation in the infants was the result of much larger binocular VEP amplitudes, while monocular VEP amplitudes were equivalent to those of stereonormal and stereodeficient adults. These results support the hypothesis that VEP amplitude is mediated by two independent pools of monocular cortical neurons and that binocular VEP amplitude in stereonormal and stereodeficient adults saturates at a lower level than in infants. Thus, it is hypothesized that binocular VEP summation is not representative of the activation of binocular cortical neurons.

Adult↗
PubMed1985

Frequency and intensity discrimination in human infants and adults.

Frequency and intensity DLs were measured in 26 human infants (ages 7-9 months) and six young adults using a repeating standard "yes-no" operant headturning technique and an adaptive staircase (tracking) psychophysical procedure. Subjects were visually reinforced for responding to frequency increments, frequency decrements, intensity increments, or intensity decrements in an ongoing train of 1.0-kHz tone bursts, and stimulus control was monitored using randomly interleaved probe and catch trials. Infants were easily conditioned to respond to both increments and decrements in frequency, and DLs ranged from 11-29 Hz, while adult DLs ranged from 3-5 Hz. Infants also easily discriminated intensity increments, and DLs ranged from 3-12 dB, while adult DLs ranged from 1-2 dB. No infants successfully discriminated intensity decrements, although adults experienced no difficulty with this task and produced DLs similar to those for increments. The apparent inability of infants to discriminate intensity decrements suggests that the infant CNS may not be well adapted to monitor rate decreases in populations of peripheral auditory neurons.

Acoustic Stimulation↗
PubMed1985

Pupillary measures of binocular luminance summation in infants and stereoblind adults.

Preverbal infants and children with ocular misalignments do not perform well on standard clinical measures of binocular function which require accurate alignment of the eyes. In 1983, Birch and Held described a pupillary measure of binocular luminance summation that could be used to assess binocular function in strabismic infants. They reported a correlation between the onset age of stereopsis and the onset age of binocular luminance summation, with both emerging at the end of the fourth postnatal month. Using a similar pupillary technique, we measured significant levels of binocular luminance summation in infants as young as 2 mo of age, as well as in stereoblind adults. In addition, the infant's pupillary system, in comparison to the adult's, showed reduced magnitudes and increased latencies to luminance increments. The sensitivity of the pupillary system to luminance increments provided a better predictor of binocular luminance summation (Pearson r = 0.88) than did stereoscopic performance (Pearson r = 0.43). These data suggest that developmental changes in the pupillary system itself, rather than factors intrinsic to binocular vision, may have been the source of the correlation between binocular luminance summation and stereopsis reported by Birch and Held.

Adult↗
PubMed1984

Infant discrimination of two- and five-formant voiced stop consonants differing in place of articulation.

According to recent theoretical accounts of place of articulation perception, global, invariant properties of the stop CV syllable onset spectrum serve as primary, innate cues to place of articulation, whereas contextually variable formant transitions constitute secondary, learned cues. By this view, one might expect that young infants would find the discrimination of place of articulation contrasts signaled by formant transition differences more difficult than those cued by gross spectral differences. Using an operant head-turning paradigm, we found that 6-month-old infants were able to discriminate two-formant stimuli contrasting in place of articulation as well as they did five-formant + burst stimuli. Apparently, neither the global properties of the onset spectrum nor simply the additional acoustic information contained in the five-formant + burst stimuli afford the infant any advantage in the discrimination task. Rather, formant transition information provides a sufficient basis for discriminating place of articulation differences.

Child Language↗
PubMed1984

Fixational eye movements and autokinesis in amblyopes.

Eye movements were recorded from amblyopic and non-amblyopic eyes during monocular viewing of a small target on either a patterned or a patternless background. A continuous measure of autokinesis was also obtained. The variance in eye position was greater in amblyopic eyes than in non-amblyopic eyes. The presence of a patterned background did not reduce the variance in eye position of amblyopic eyes. Autokinesis was greater in amblyopic eyes, but was not correlated with the eye movements. A patterned background significantly reduced the magnitude of autokinesis in amblyopic eyes. These results provide support for the hypothesis that a patterned background improves the accuracy of visual direction by reducing spurious extraretinal signals.

Amblyopia↗
PubMed1983

Dark vergence and dark accommodation in human infants.

Vergence angle and accommodative state were assessed photographically in 3-, 6-, and 12-month old infants. In the dark, fluctuations of vergence and accommodation were generally uncorrelated among all groups. The vergence-accommodation functions obtained in the dark had a mean slope of 0.04. These findings provide evidence in infants for an uncoupling of vergence and accommodation in the absence of patterned retinal input.

Accommodation, Ocular↗
PubMed1982

Some effects of laboratory training on identification and discrimination of voicing contrasts in stop consonants.

For many years there has been a consensus that early linguistic experience exerts a profound and often permanent effect on the perceptual abilities underlying the identification and discrimination of stop consonants. It has also been concluded that selective modification of the perception of stop consonants cannot be accomplished easily and quickly in the laboratory with simple discrimination training techniques. In the present article we report the results of three experiments that examined the perception of a three-way voicing contrast by naive monolingual speakers of English. Laboratory training procedures were implemented with a small computer in a real-time environment to examine the perception of voiced, voiceless unaspirated, and voiceless aspirated stops differing in voice onset time. Three perceptual categories were present for most subjects after only a few minutes of exposure to the novel contrast. Subsequent perceptual tests revealed reliable and consistent labeling and categorical-like discrimination functions for all three voicing categories, even though one of the contrasts is not phonologically distinctive in English. The present results demonstrate that the perceptual mechanisms used by adults in categorizing stop consonants can be modified easily with simple laboratory techniques in a short period of time.

Adult↗
PubMed1981

Discrimination of voice onset time by human infants: new findings and implications for the effects of early experience.

Discrimination of voice onset time (VOT) by 6--12-month-old infants was examined in 2 experiments. An operant head-turning technique assessed discrimination along a synthetic VOT continuum ranging from -70 msec to +70 msec. Infants from an English-speaking environment provided reliable within-subject evidence for discrimination of VOT contrasts located at both the plus and minus regions of the VOT continuum. These results provide strong evidence that infants from an English-speaking environment are capable of discriminating VOT contrasts that are not phonemic in English. Threshold delta VOT values indicated that the infants were more sensitive to VOT differences in the plus region of the VOT continuum than in the minus region. Threshold delta VOT values from English-speaking adults indicated greater sensitivity at every location along the VOT continuum. In addition, the adults showed heightened sensitivity to VOT differences near the voiced-voiceless boundary in the plus region of the VOT continuum, a finding that was not evident in the infants' data.

Adult↗
PubMed1980

Stereopsis in human infants.

Stereoscopic depth perception was tested in human infants by a new method based on attracting the infant's attention through movement of a stereoscopic contour formed from a dynamic random-element stereogram. The results reveal that stereopsis emerges at 3 1/2 to 6 months of age, an outcome consistent with evidence for rapid postnatal development of the visual system.

Age Factors↗
PubMed1980

Effects of early linguistic experience on speech discrimination by infants: a critique of Eiler, Gavin, and Wilson (1979).

In a recent report in this journal, Eilers, Gavin, and Wilson (1979) presented discrimination data obtained from 2 groups of infants exposed to different language-learning environments. The results showed differences in voice onset time (VOT) discrimination between Spanish and English infants, suggesting an effect of early linguistic experience. A critique of this study indicates that such conclusions about the effects of early experience on speech perception are unwarranted on both methodological and conceptual grounds. Methodological flaws include the absence of reliable statistical analyses and the failure to guard against experimenter bias effects. Conceptual flaws involve the erroneous interpretation of failures to discriminate certain selected speech contrasts. Inferences concerning the developmental course of speech perception in young infants based on the results of the Eilers et al. study need to be interpreted cautiously in light of these serious criticisms.

Discrimination Learning↗