Dichoptic plaids may rival, but their motions can integrate.

When the eyes view incompatible images, binocular rivalry usually results: image constituents in corresponding parts of the monocular visual fields are not perceived simultaneously. We asked naive undergraduates to view dichoptic, dioptic, and monoptic plaids. The dichoptic images evoked strong binocular rivalry when contrast was high, especially if the component gratings were set in motion. Nevertheless, the subjects' visual systems integrated the motion information across the two eyes, producing a unitary motion percept that did not reflect the image in either eye alone. By manipulating the relative spatial scale of the gratings, we affected how well the motion cohered: the results were remarkably similar between dichoptic and traditional dioptic plaids. By manipulating the relative speed of the gratings, we systematically affected the perceived direction of motion of the plaids; these results were also remarkably similar for dichoptic and dioptic plaids. Thus, the motion analysis of dichoptic and dioptic plaids is proceeding according to very similar rules, even though the dichoptic images are incompatible and evoke binocular rivalry.

An event-based analysis of the coordination of early infant vocalizations and facial actions.

This study used an event-based approach to provide empirical evidence regarding the nature of coordination in 3- and 6-month-old infants. Vocalizations and facial actions of 12 normally developing infants interacting with their caregivers were coded. Coded vocalizations and facial actions were considered coordinated when they temporally overlapped. Results indicate that infants coordinated their vocalizations and facial actions more than expected by chance. Coordinated events were governed by 2 sequence patterns. When 2 communicative events were temporally associated across modalities, 1 event tended to be completely embedded within the other, and vocalizations tended to end before facial actions. This study provides new information about how infant communication is structured, confirms results from other coordination studies, and describes a new method for analysis of event-based data.

Late onset canonical babbling: a possible early marker of abnormal development.

By their 10th month of life, typically developing infants produce canonical babbling, which includes the well-formed syllables required for meaningful speech. Research suggests that emerging speech or language-related disorders might be associated with late onset of canonical babbling. Onset of canonical babbling was investigated for 1,536 high-risk infants, at about 10-months corrected age. Parental report by open-ended questionnaire was found to be an efficient method for ascertaining babbling status. Although delays were infrequent, they were often associated with genetic, neurological, anatomical, and/or physiological abnormalities. Over half the cases of late canonical babbling were not, at the time they were discovered associated with prior significant medical diagnoses. Late canonical-babbling onset may be a predictor of later developmental disabilities, including problems in speech, language, and reading.

An adaptive psychophysical method for subject classification.

In psychophysical experiments, one's goal is usually to measure some continuous parameter hypothesized to determine the statistical properties of a subject's responses. Methods are well developed that adaptively manipulate stimulus characteristics in such a way that the reliability of the parameter estimate is maximized. However, such methods are inapplicable in situations in which the goal is to assign subjects to discrete categories, rather than to measure a continuous parameter. This paper introduces a technique that is directly applicable to efficient categorization and that adaptively manipulates stimulus characteristics in such a way that the information obtained from each trial is maximized. This technique is based on the principle of minimum estimated expected entropy, whereby stimulus parameters on each trial are chosen in order to minimize the estimated expected entropy of the a posteriori probability distribution that expresses how likely a subject is to belong to each of a group of mutually exclusive categories. A sample implementation of the technique--the classification of infant subjects according to their audiograms--is then described and evaluated via computer simulation.

Development of precursors to speech in infants exposed to two languages.

The study of bilingualism has often focused on two contradictory possibilities: that the learning of two languages may produce deficits of performance in each language by comparison with performance of monolingual individuals, or on the contrary, that the learning of two languages may produce linguistic or cognitive advantages with regard to the monolingual learning experience. The work reported here addressed the possibility that the very early bilingual experience of infancy may affect the unfolding of vocal precursors to speech. The results of longitudinal research with 73 infants aged 0;4 to 1;6 in monolingual and bilingual environments provided no support for either a bilingual deficit hypothesis nor for its opposite, a bilingual advantage hypothesis. Infants reared in bilingual and monolingual environments manifested similar ages of onset for canonical babbling (production of well-formed syllables), an event known to be fundamentally related to speech development. Further, quantitative measures of vocal performance (proportion of usage of well-formed syllables and vowel-like sounds) showed additional similarities between monolingual and bilingual infants. The similarities applied to infants of middle and low socio-economic status and to infants that were born at term or prematurely. The results suggest that vocal development in the first year of life is robust with respect to conditions of rearing. The biological foundations of speech appear to be such as to resist modifications in the natural schedule of vocal development.

Longitudinal speech perception performance of young children with cochlear implants and tactile aids plus hearing aids.

Nineteen profoundly deaf children who utilize either cochlear implants (CIs) or multichannel tactile aids plus hearing aids (T + HAs) and who were enrolled in a full-day educational program that specializes in the use of sensory aids were evaluated using a battery of speech perception tests either developed in house or chosen because they were part of a standard battery of tests developed for children with sensory aids. The tests were organized into four perceptual levels ranging from pattern perception at level one to open set word identification at level four. For each level, data were analyzed for changes over time and for differences between performance of CI children and those using T + HAs. The results indicate that overall, across levels, both groups improved significantly over time but no differences were found between users of T + HAs and CIs at any level.

Poor stereopsis can support size constancy in albinism.

PURPOSE: The size of a retinal image is inversely related to the distance to the object that generates the image. Normal subjects therefore exhibit size constancy, in which the perceived size of an image is scaled according to its perceived distance. Albinos usually have such poor binocular vision that they perform very poorly on clinical tests for stereopsis. To investigate the functional consequences of this poor stereopsis, we investigated whether stereopsis in these subjects could support size constancy. METHODS: The stereothresholds of 10 albinos and 12 normal control subjects were measured. The presence of absence of size constancy was investigated by having subjects equate the subjective size of stereoscopically presented images whose image disparity indicated that they were at different distances. RESULTS: Laboratory results indicated that eight albinos (including five whose clinical tests indicated a lack of stereopsis) had measurable stereopsis of several thousand are seconds or better. Of these, four also exhibited size constancy. CONCLUSIONS: Albinos who do not demonstrate stereopsis on clinical tests can have stereoscopic perception that commonly used clinical tests do not detect. Moreover, some of these patients even use this poor stereopsis in judging the size of stereoscopically presented images.

A longitudinal evaluation of the speech perception capabilities of children using multichannel tactile vocoders.

Thirty children (mean age 6:11, range 4:3 to 11:0, SD = 2:3) with profound hearing impairments were followed longitudinally over a 3-year period and evaluated every 6 months with a battery of speech perception tests. The battery spanned several levels of perception, from pattern perception to open-set word recognition. The children were all enrolled in a single full-day educational program that used multichannel tactile aids in addition to hearing aids. Testing was conducted in Auditory alone (A), Tactile plus Auditory (TA), Tactile alone (T), and in one instance, Tactile plus Auditory plus Vision (TAV) conditions because the primary interest of the work was the relationship between auditory and tactile training on perception. Results indicated that children's performance improved with age, with the oldest children achieving open-set speech recognition in the TA condition. Performance in the TA condition generally exceeded that in both A and T conditions. Outcomes were compared to those from two studies in the literature for children of similar age with cochlear implants and tactile aids on the same tests. Results suggest that performance of children who had cochlear implants for an average of 21 months was similar to TA and TAV performance of children in the present study who had tactile experience over a similar period.

Relations of motor and vocal milestones in typically developing infants and infants with Down syndrome.

We measured the ages at which typically developing infants and infants with Down syndrome achieved an important vocal milestone (canonical babbling), a rhythmic motor milestone (hand-banging), and six other motor milestones. The interrelations of the milestone onsets, and their relations with Down syndrome, were assessed quantitatively. Hand-banging and canonical babbling were associated and were somewhat delayed by Down syndrome. Stepping, standing, sitting, and creeping/crawling were associated and were severely delayed by Down syndrome. Rolling and reaching were also delayed by Down syndrome, though they were not strongly associated with other milestones or with one another. These results suggest that the rhythmic behaviors (canonical babbling and hand-banging) may be internally linked by common neuromuscular underpinnings and that the postural behaviors may be similarly linked.

Monocular dot-density cues in random-dot stereograms.

In the original random-dot stereograms (RDSs) invented by Julesz, binocular disparity could only take on values that were integral multiples of dot width. The other common method for constructing RDSs (the projection method) relaxes this restriction. However, the projection method can introduce dot-density cues into the monocular images. When polar projection is employed, density variation is introduced as an expression of perspective cues; when parallel projection is employed, there are no perspective cues, but density variation is nonetheless introduced whenever disparity varies as a function of horizontal position. de Vries, Kappers, and Koenderink [(1994) Vision Research, 34, 2409-2423] proposed to minimize the density cues by selecting half of the random dots from a uniform random distribution in the right-eye image, projecting them onto the cyclopean surface, and then projecting them back to the left eye image and vice versa. In this paper the precise nature of the density cues introduced by the projection method, and by de Vries et al.'s modification of that method, are derived. It is also shown that the projection method and its modification have very similar density cues near the medial sagittal plane when polar projection is employed, and that they have identical density cues over the entire random-dot field when parallel projection is employed.

Selectivity of cyclopean masking for the spatial frequency of binocular disparity modulation.

Previous studies have presented evidence for the existence of channels tuned to the spatial frequency (SF) of binocular disparity modulation. Bandwidths reported for masking curves were extremely narrow, possibly because of off-frequency viewing, whereby observers can best detect a signal with a channel tuned to an SF on the opposite side of the signal from the masker's SF, rather than with a channel tuned directly to the signal's SF. Herein are reported the results of four detection experiments. Experiment 1 measures unmasked threshold for detection of a cyclopean grating. Experiments 2-4 are masking experiments. Experiment 2 demonstrates that threshold for detection of a cyclopean grating is proportional to the intensity of masking noise, which is consistent with the operation of linear channels. Experiments 3 and 4 demonstrate that masking curves are narrower when obtained with narrowband-noise maskers than when obtained with notched-noise maskers, which render the off-frequency viewing ineffective. Implications for understanding the processing of cyclopean images are discussed.