Oculomotor responses to step-ramp targets by young human infants.

Previous research has shown that the smooth pursuit system in early infancy is quite immature. Infants' tracking of a single, small target moving at velocities greater than 10 deg/sec is almost entirely saccadic until the end of the second postnatal month. The emergence of smooth pursuit is characterized by low gain (less than 0.5) and frequent saccadic intrusions. To provide a quantitative description of pursuit to relatively slow target velocities, 10 infants ranging in age from 7 to 11 weeks viewed a 2 deg target that was stepped 5 to 10 deg from screen center and then ramped back to screen center and 10 deg beyond at a constant velocity of 3, 6 or 12 deg/sec. Smooth pursuit was observed even in the youngest infant whose segments of pursuit between saccades were up to 5 sec in duration. At the slowest target velocity, mean pursuit gain across infants was 0.50, while at 6 and 12 deg/sec mean pursuit gain was 0.25 and 0.11. This systematic decrease in pursuit gain with increasing target velocity implies that pursuit velocity was invariant across the three target velocities. These findings suggest that smooth pursuit can be generated consistently by the end of the second postnatal month, but that it is slow and uncalibrated to the velocity of the target.

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.

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.

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.

Middle-latency and 40-Hz auditory evoked responses in normal-hearing subjects: click and 500-Hz thresholds.

Click and 500-Hz tone-burst thresholds were determined by four independent judges from sequentially recorded auditory brain stem responses--middle-latency responses (ABR-MLR)--and from 40-Hz event-related potentials (ERP) in 10 normal-hearing subjects. The thresholds determined from the two electrophysiologic methods were compared to each other and to behavioral pure-tone thresholds by means of matched-pair t tests (alpha less than or equal to .016 for each comparison). Thresholds estimated from both techniques closely approximated behavioral audiometric thresholds. The general trend was for the 40-Hz ERP thresholds to be lower than the MLR thresholds. However, the statistical analysis indicated that the differences between the two electrophysiologic thresholds and pure-tone audiometric thresholds were not significant. At threshold, the amplitudes of the 40-Hz ERPs were almost twice as large as the MLR amplitudes for clicks and only slightly larger than the MLR amplitudes for the 500-Hz tone-bursts. It was concluded that the MLR and the 40-Hz ERP techniques are equally viable procedures for threshold estimation in adults.

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.

Assessment of electromagnetic characteristics of the Willeford Central Auditory Processing Test Battery.

Electromagnetic characteristics of eight tape recordings of the Willeford Central Auditory Processing Test Battery were assessed. Measurements indicate that when recording levels are referenced to the calibration tone preceding a given subtest of that battery, significant intertape differences, interest differences, and interchannel differences in the recording levels of test items exist. Mean recording levels of items used in the Rapidly Alternating Speech Perception, Low-Pass Filtered Speech, and Competing Sentences subtests typically were within 10 dB of the reference tone. Recording levels for the Binaural Fusion subtest yielded intertape differences of as much as 26.5 dB. Given the large intertape inconsistencies in recording levels, extreme caution should be exercised in the use of these recordings.

Incidence of hearing loss among geriatric nursing-home residents.

Of 285 residents in 4 Montana nursing homes, pure-tone ac HTLs were collected on 259 ears of 151 Ss, aged 54-95 yrs (mn: 80.6 yrs) who were able and willing to participate. Only 6% of ears were normal [PTA (.5, 1, 2 kc/s) less than 25 db], 11% had mild losses (25-45 db), 13% had moderate (45-65 db), 35% had high-frequency slope beginning at 2 kc/s, and 35% had severe or profound losses (greater than 65 db). Of 175 ears of 92 Ss completing tympanometry, 85% had normal peak-pressure points, 9% were mildly positive/negative, and 7% were abnormal. Of 116 ears from 62 Ss completing contralateral acoustic reflex study, only 58% exhibited reflexes. Of 59 ears from 34 Ss completing ipsilateral acoustic reflex study, only 39% exhibited reflexes. 48% of ears exhibited abnormal otoscopic findings. Only 17 Ss reported owning a hearing aid (though for half the Ss Medicaid allowed payment for such aids). Of 13 aids actually inspected, all were malfunctioning in correctable ways. Audiological referrals were made for 94% of the 151 Ss, and medical referrals for 58%. These data corroborate other studies on the low status of audiological services in such populations.

Assessment of stereopsis in human infants.

A new method for testing stereopsis in infants is described for use in the early assessment of binocular function. Four 6- and 12-month-old infants were presented with a dynamic random-element stereogram generated on a color television monitor. A stereoscopic form was moved laterally, either left or right, to elicit the visual attention of the infant. An observer, unaware of the direction of form movement, made a forced-choice judgment of the direction of form displacement based on information gleaned from observations of the infant's behavior. The observer's performance for all three age groups exceeded chance levels of responding (p < 0.001). Individual infants within each age group also provided strong evidence of stereopsis. The applicability of the method for the screening of binocular anomalies is discussed.

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.

Inbreeding and copulatory behavior in house mice: a further consideration.

Comparisons were made of the copulatory behavior of randomly bred (one population: WRL) and inbred wild (five strains: PAA, ab, ac, ad, and PAE) male house mice. All inbred and randomly bred stocks were derived from a single foundation population. The inbred males tended to have shorter latencies to the first mount and intromission, longer latencies to ejaculation, and more preejaculatory mounts and thrusts than randomly bred males. All these effects parallel those observed in a previous study in which a wild population was compared with various domestic inbred strains. If inbreeding depression is related to adaptive significance, these data suggest that, although rapid initiation of copulation in a novel environment may not be adaptive, it may be adaptive for mice to ejaculate rapidly once copulation is initiated.

Integrating verbal quantitative information in linear orderings.

Subjects learned and answered questions about four-term linear orderings described in paragraphs of text. Spacing along the dimension employed was varied by using verbal quantifiers ("just barely," "moderately," and "very much"). After learning the quantitative information, performance on ordinal information varied as a function of the quantitative difference between terms in the ordering. Reaction time was faster for large quantitative differences than for small quantitative differences. This result indicates that vague verbal quantitative information is integrated into the memory representation for an ordering and that such quantitative information does affect test performance.