Delayed recognition memory for orientation by human infants.

The familiarization/novelty preference paradigm was employed to study the effect of a delay (between the end of the familiarization phase and the beginning of the test phase) on discrimination of the orientation of square-wave gratings by 2- and 3-month-old human infants. Three stimulus pairs were studied: horizontal-vertical, non-mirror-image obliques, and mirror-image obliques. The data indicate that the members of the oblique-oblique stimulus pairs are confused in memory to a greater extent than the members of the horizontal-vertical stimulus pair. These findings are consistent with P.C. Bomba's (1984, Journal of Experimental Child Psychology, 37, 609-636) recent report that infants respond to the orientation of a visual stimulus in a categorical-like manner.

Contextual effects in infant visual perception.

A familiarization/preference technique was used to assess the ability of three- and four-month-old infants to discriminate line segments that differed in orientation. Discrimination was found to be significantly better, as evidenced by a greater preference for the novel stimulus, when the line segments were embedded in a redundant contextual frame than when they were presented alone. However this effect could not always be unambiguously interpreted; under some stimulus conditions, a strong stimulus preference may have caused the novelty effect. It is concluded that perception in infants is, at least in part, organized and, as in adults, involves more than a simple feature-by-feature analysis of information.

Discrimination of orientation by human infants.

Successive discrimination of suprathreshold gratings of different orientations by two-month-old infants was tested with the use of a type of familiarization-novelty paradigm. Infants showed clear discrimination between horizontally and vertically oriented gratings. Infants failed, however, to discriminate mirror-image obliques from each other and also failed to discriminate nonmirror-image obliques. Considered along with previous demonstrations in children and adults of a greater confusability of oblique grating pairs relative to that of the horizontal and vertical pair, these findings indicate that this differential confusability of orientation is, at least in part, manifest in humans by two months of age.

Speech perception in infants.

Discriminiationi of synthetic speech sounds was studied in 1- and 4-month-old infants. The speech sounds varied along an acoustic dimension previously shown to cue phonemic distinctions among the voiced and voiceless stop consonants in adults. Discriminability was measured by an increase in conditioned response rate to a second speech sound after habituation to the first speech sound. Recovery from habituation was greater for a given acoustic difference when the two stimuli were from different adult phonemic categories than when they were from the same category. The discontinuity in discrimination at the region of the adult phonemic boundary was taken as evidence for categorical perception.

Visual reinforcement of nonnutritive sucking in human infants.

High-amplitude sucking was studied as a conditioned operant response reinforced by visual feedback in 4-and 12-month infants. Typicalresponse acquisition and extinction effects were obtained. With the 12-month infants the conditioned sucking rates were influenced by amounts of redundancy in the visual reinforcers.