Perception of internal elements of compound figures by one-month-old infants

Previous research has shown that infants younger than 2 months frequently concentrate their attention on peripheral or external features of visual stimuli and that they do not appear to process the internal elements of a compound visual stimulus composed of a simple geometric figure enclosed in a larger figure. A visual habituation-dishabituation paradigm was used to determine whether 1-month-old infants would process internal information if the internal elements of the stimulus were patterns often found to be preferred by young infants. Four groups of eight infants each were habituated to a compound stimulus consisting of a square or triangle surrounding a checkerboard or bull's-eye. Following habituation each group was presented with one of four types of stimulus: the identical stimulus (control group), a stimulus differing only in the internal component, a stimulus differing only in the external component, or a stimulus differing in both components. The results of the present study suggest that when the internal element of a compound stimulus is a highly preferred or salient stimulus, the young infant will process information about its characteristics.     

Newborn's discrimination among mid- and long-wavelength stimuli

Recent anatomical and behavioral evidence suggests that important visual functions like color vision may be severely limited at birth. Therefore, we examined human newborns' ability to discriminate among stimuli of different wavelength by habituating them to a 16 degrees chromatic square of widely varying luminance (as wide as 1.1 log cd/m2) and then testing for recovery of habituation to a different chromatic square of the same size. In the first experiment, newborns showed evidence of recovery to a 650-nm (peak wavelength) red square after habituating to 545-nm green squares, but they did not recover to the red or the green after habituating to 585-nm yellow squares. In a second experiment using the same procedure, newborns did not show evidence of discriminating the 650-nm red from the 545-nm green when the stimulus size was reduced to 8 degrees. These data suggest that human newborns are capable of making a chromatic discrimination within the spectral region above 540 nm (the Rayleigh region) but their ability is limited to chromatic stimuli of very wide spectral separation and of very large size. Possible neurological bases underlying this immaturity are discussed.     

A neural activity interpretation of luminance effects on infant pattern preferences

Visual pattern preferences were established for 9- and 13-week-old infants (N = 96) using stimuli varying in contour density presented either at a low, moderate, or high luminance level. Age differences in the maximally preferred patterns across stimuli and luminance levels indicated that luminance interacts with contour density in determining stimulus preference functions for a given age. A neural activation model based on synchronous neural activity was advanced to describe these results.     

Contrast and spatial frequency components in visual preferences of newborns

A preferential-looking procedure was used to investigate newborns' responses to square-wave gratings varying in spatial frequency and contrast. A preliminary study confirmed that the gratings used in the experiment were suprathreshold. In the experiment newborns' preference for a grating of 0.1 cycle deg-1 within the peak contrast sensitivity range was examined. Reduction in the contrast of this grating led to a transfer of the preference to a high-contrast grating of the same space-averaged luminance with a spatial frequency outside this range (0.42 cycle deg-1). The findings are discussed with reference to the role of the contrast sensitivity function in pattern preferences of newborns: it is suggested that contrast and spatial frequency interact in determining pattern preferences.     

Binocular fixation in the newborn baby.

Three experiments are reported in which the newborn baby's ability to fixate binocularly was investigated, using the corneal reflection technique for measuring eye fixation position. Two criteria for consistent binocular fixation were assessed. These are (1) the two eyes will be optically more divergent when fixating more distant targets, and (2) each eye will be scored as being on-target when corrections for the expected deviations of the pupil center from the fixated stimulus are introduced.In the first experiment vertical arrays of lights were separately shown at distances of 10 and 20 in. from the subjects' eyes (with the retinal image size and luminance of the stimuli held constant). The 12 newborns who gave results at both viewing distances reliably converged to both stimuli, the optical divergence of the pupil centers of the eyes increasing with presentation of the more distant stimulus. In Expt 2 similar stimuli at 5 and 10 in. from the eyes were shown. It was again the case that the subjects reliably converged to the stimulus at 10 in. This was no so for the stimulus at 5 in., and many subjects fixated this stimulus with monocular vision. The failure to converge is probably due to an inability to accommodate to this near distance. In Expt 3 different stimuli (a vertical strip of light, an outline triangle and square, and an array of squares) were presented a constant distance (10 ± 1 in.) from the eyes. The majority of the 15 subjects binocularly fixated all three stimuli: for those subjects who failed to converge consistently to these stimuli the observed alternatives to binocular fixation were monocular fixation, divergent strabismus, and a third category of response that is most probably an indication of inattention to the stimulus. It can be concluded that the newborn baby possesses the ability to fixate binocularly an appropriately presented stimulus, and has the basic requirements for binocular vision.     

Visual processing of stimulus compounds in newborn infants

An experiment is described in which newborn infants' processing of stimulus compounds was investigated. After familiarization to two alternately presented stimuli which differed in colour and orientation, the newborns showed significant preferences for a stimulus which had a novel colour/orientation combination: the novel stimulus was produced by recombining features of the stimuli used for familiarization. This finding argues against the view that infants initially process separate components, or parts, of visual stimuli and are only able to attend to the correlations between them after about 3 months of age. Rather, the ability to process and remember stimulus compounds is present at birth.     

Heart-rate and electrodermal orienting responses to visual stimuli differing in complexity

Orienting response (OR) theory predicts that amount of information in the stimulus, or stimulus complexity, should be an important determinant of OR elicitation and habituation, more intense and more slowly habituating ORs being expected to complex than to simple stimuli. This prediction was tested in an experiment where subjects were exposed to simple and complex visual stimuli in randomized order, while heart-rate and skin conductance were measured. Complex stimuli evoked a more pronounced deceleratory heartrate response than did simple stimuli. However, the two conditions did not differ in rate of habituation of this response. For skin conductance responses, on the other hand, the complex stimulus took more trials than the simple stimulus to reach habituation, whereas the two conditions did not differ in response magnitude. Thus, the hypothesis of more intense orienting to complex stimuli was supported by the heart-rate data, and that of slower habituation to complex stimuli, of the skin conductance data.     

Infant perception of static two-dimensional transparency information

The present habituation – dishabituation study focused on infants' perception of static two-dimensional transparency displays. Infants 4 and 8 months of age were habituated to a transparency display. In this stimulus, each corner of a semi-transparent square surface covered a quadrant of a circle. During the posthabituation period, the infants were presented with the semi-transparent square overlay from the habituation display and a (non-transparent) square area cut out of the habituation stimulus. The 8-month-olds looked significantly longer at the non-transparent surface, meaning that they apparently recognized the other test pattern as the semi-transparent filter they had also seen during the habituation trials, and that they regarded the non-transparent test target as being novel. In contrast, the younger participants did not exhibit a novelty preference during the posthabituation trials. Control conditions tested the impact of spontaneous stimulus preferences on the results. The findings are discussed within the framework of infant pictorial depth perception. They provide further evidence for the hypothesis that infants' sensitivity to pictorial depth cues emerges between 4 – 5 and 7 – 8 months of life.     

The development of orientation categories between 2 and 4 months of age

Recent research has indicated that infants are capable of responding to stimuli in a manner indicating that they categorize them. Infant perception of orientation was examined within a framework of categorization. In one experiment, it was shown that 4-month-old infants generalized habituation from one range of oblique grating stimuli to another, consistent with the interpretation that any two oblique stimuli were perceived as more similar than a vertical and an oblique. Four-month-old infants' generalization was not due to a simple inability to discriminate between obliques (Experiment 2) so the results of Experiment 1 reflect in large part true categorization behavior and not categorical perception. Results for 2- and 3-month old infants suggest that "vertical" serves as a reference stimulus in infant orientation perception such that gross distinctions between vertical and nonvertical precede the development of the "oblique" category. The category boundary between oblique and vertical did not successfully predict better between-than within-category discrimination in 4-month-old infants (Experiment 3) under the conditions of these experiments.     

Locus of habituation in the human newborn

There is some controversy concerning the youngest age at which an infant will habituate to a visual stimulus or will prefer a novel to a familiar pattern. One suggestion has been that apparently successful reports of habituation and dishabituation in the newborn baby are attributable to retinal adaptation. This interpretation was tested in two experiments. In both experiments monocular conditions of viewing were used: newborns were habituated with one eye as the 'seeing' eye, and posthabituation novelty preferences investigated with the other eye. Significant preferences were found both for a novel colour (experiment 1) and for a novel shape (experiment 2), which implies that a retinal-adaptation model can be ruled out. It is suggested that the habituation effects and the subsequent novelty preferences found in the experiments are most reasonably interpreted as a function of memory formation, and evidence is presented for the storage of visual experience from birth. The results also demonstrate some form of binocular interaction in the newborn.     

Habituation and the human evoked potential

Habituation of human scalp-recorded cerebral evoked potentials was studied in response to auditory and visual repetitive stimuli of different intensities. Changes in magnitudes of evoked potentials with stimulus repetition were examined according to the parametric characteristics of habituation, generalization, and dishabituation. In addition, tests of the predictions of two theories of habituation were made regarding the degree and direction of intensity generalization of habituation. Both auditory and visual evoked potentials exhibited decrements in response magnitudes across the repetitive stimuli consistent with the parametric criteria of habituation. Early evoked potential peak components showed a pattern of intensity generalization of habituation consistent with the predictions of the dual-process theory of habituation. Intensity generalization of late evoked potential peak components occurred in a manner more consistent with the predictions of the stimulus comparator theory of habituation. These results provide further evidence that evoked potentials can be used as electrophysiological indexes of plasticity in humans.     

Form perception at birth: Cohen and Younger (1984) revisited

Cohen (1988; Cohen & Younger, 1984) has suggested that there is a shift in the perception of form sometime after 6 weeks of age. Prior to this age infants can remember the specific orientations of line segments, but cannot process and remember the angular relations that line segments can make. Experiment 1 used simple line stimuli with newborn infants to test this suggestion. Following habituation to a simple two-line angle the newborns dishabituated to a change of orientation but not to a change in angle, confirming Cohen and Younger's suggestion that orientation is a powerful cue in early shape perception. In Experiments 2 and 3 newborns were familiarized either to an acute or to an obtuse angle that changed its orientation over trials. On subsequent test trials the babies gave strong novelty preferences to a different angle. Alternative interpretations of the results are discussed, but these experimental findings are compatible with the suggestion that newborns can quickly learn to process angular relations, and that rudimentary form perception may not be dependent on a lengthy period of learning and/or maturation for its development.     

Stimulus energy does not account for 2-month-olds' face preferences

We examined the determinants of 2-month-olds' preferences among facelike and abstract patterns. Observed preferences were compared with the predictions of two preference models--one based on stimulus energy (as measured by the amplitude spectrum) and the other based on stimulus structure (as measured by the phase spectrum). It is known that the phase spectrum is the primary determinant of perceived identity to adults. Twenty-five 2-month-olds saw six pairings of four patterns: a schematic face, a lattice, a pattern composed of the amplitude spectrum of the lattice and the phase spectrum of the face, and a pattern composed of the amplitude spectrum of the face and the phase spectrum of the lattice. Only patterns with the face's phase spectrum look facelike to adults. Unlike the preferences of newborns (Kleiner, 1987), 2-month-olds' preferences could be predicted from the phase spectrum but not from the amplitude spectrum. In other words, the 2-month-olds preferred the patterns that looked facelike to adults. These results offer clear evidence that 2-month-olds' preferences for facelike patterns are not governed by stimulus energy.     

Distinguishing novelty and familiarity effects in infant preference procedures

This paper considers possible problems researchers might face when interpreting the results of studies that employ variants of the preference procedure. Infants show a tendency to shift their preference from familiar to novel stimuli with increasing exposure to the familiar stimulus, a behaviour that is exploited by the habituation paradigm. This change in attentional preference with exposure leads us to suggest that researchers interested in infants' pre‐experimental or spontaneous preferences should beware of the potentially confounding effects of exposing infants to familiarization trials prior to employing the preference procedure. The notion that infant attentional preference is dynamic also calls into question the use of the direction of post‐familiarization preference per se when interpreting the knowledge or strategies available to infants. We look into the results of a cross‐modal word learning study to show how the interpretation of results may be difficult when infants exhibit a significant preference in an unexpected direction. As a possible solution to this problem we propose that significant preferences in both directions should be sought at multiple intervals over time. Copyright © 2004 John Wiley & Sons, Ltd.     

Development of orientation discrimination in infancy

It has previously been found by us, with a visual evoked potential (VEP) measure, that orientation discrimination of dynamic patterns in infants can be demonstrated from around 6 weeks after birth. Experiments are reported in which orientation discrimination was measured behaviourally, in two infant control habituation procedures, with both dynamic and static patterns. When dynamic patterns identical to those in our previous VEP studies were used, the first positive evidence of orientation discrimination was found at around 6 weeks postnatally. The time course of both the VEP and the behavioural measures was similar. However, with static patterns, evidence of orientation discrimination by newborns was found if the infants were allowed to compare the habituated and novel orientations in a paired simultaneous comparison after habituation, but was not found when the habituated and novel stimulus were presented sequentially. The positive evidence of orientation discrimination in newborns supports the hypothesis that some form of orientationally tuned detectors can be used for discrimination of static patterns at birth. However, some developmental change over several weeks seems to be required before a positive electrophysiological VEP response can be measured for dynamic patterns changing in orientation.     

Crossmodal learning in newborn infants: Inferences about properties of auditory-visual events

The majority of research on infant crossmodal perception has addressed the question of whether infants 4 months and older demonstrate the ability. By contrast, the focus in the present study was on newborns and the primary goal was twofold: to determine if newborns can learn arbitrary sight-sound pairings and to evaluate possible inferences that neonates make when repeatedly presented arbitrary sight-sound pairings. Alert neonates were familiarized with toy-sound pairs using an infant-controlled habituation procedure. They were then given a violation-of-expectancy test to determine if they had learned these sight-sound pairings and drawn any inferences about certain properties of these bimodal events. Results supported the conclusion that infants just a few hours old can learn sight-sound pairings. Furthermore, the findings suggested that newborns expected sight-sound pairs to remain colocated even when they move to a new location, they recognized that the sound was an attribute of a specific object, and they recognized that a specific spatial location was not an attribute of the sight-sound pair. Thus, infants made important and correct inferences based on limited experiences with specific auditory-visual events, and they did so just after birth. Implications of these findings for theories of crossmodal perceptual development are discussed.     

One-month-old human infants learn about the social world while they sleep

Although infants display preferences for social stimuli early in their lives, we know relatively little about the mechanisms of infant learning about the social world. In the current set of studies, 1-month-old infants underwent an adapted eyeblink conditioning paradigm to examine learning to both 'social' and non-social cues. While infants were asleep, they were presented with either a 'social' stimulus (a female voice) or one of two non-social stimuli (tone or backward voice) followed by an airpuff presented to the eyelid. Infants in the experimental groups displayed increased learning across trials, regardless of stimulus type. However, infants conditioned to the 'social' stimulus showed increased learning compared to infants conditioned to either of the non-social stimuli. These results suggest a mechanism by which learning about the social world occurs early in life and the power of ecologically valid cues in facilitating that learning.     

Newborn visual attention to repeated exposure of redundant vs “novel” targets

This study was designed to test the proposition that habituation in the newborn human is specific to repetition of a single impinging stimulus. Using a group (3) by sex (2) by trials (8) repeated measures factorial design, 120 newborn infants were repeatedly presented with a single visual target (2 × 2 or 12 × 12 black and white checkerboard) or exposed to a series of different targets, and the infants’ visual fixation time was measured. Infants exposed to the multiple target series had a significantly greater mean visual fixation time than did infants repeatedly presented with a single target. However, all groups of infants displayed response decrement in fixation time with repeated target exposure. In addition, infants receiving the multiple target series displayed differential visual fixation to the stimuli, with, in general, targets of greater redundancy (Le., those having a higher degree of spatial repetition and duplication of elements) being most “preferred.” These results suggest that young human infants are receptive and responsive to stimulus change in the immediate visual environment.     

Comparison of infant and adult P300 from auditory stimuli.

Event-related brain potentials (ERPs) using auditory stimuli were recorded from 5- to 10-month-old infants and normal young adults with a passive tone sequence paradigm. A P3 (P300) component was obtained which demonstrated the same central-parietal maximum scalp distribution for both subject groups. P3 amplitude was smaller and its peak latency longer for infants compared to those of the adults across all electrode sites. P3 measures remained stable across stimulus trials indicating that ERP habituation was not occurring. Evaluation of individual subjects suggests that the P3 can be elicited from infants with auditory stimuli in a manner similar to that from adults and may serve as a useful index for the assessment of cognitive function in infants.