Cerebral asymmetry of emotion and its relationship to olfaction in infancy.

To examine the relationship between emotional development and laterality, smells differing in affective valence (predetermined by adults) were presented to 10 neonates. Each infant was presented with two positive and two negative food-related odorants, each paired with a neutral stimulus. Each pair was presented twice, once with the odorant to the right nostril and once to the left nostril. These eight trials were repeated in two blocks. In addition, control trials, where a puff of air was administered to both nostrils, were included. Head turning from midline position to presentation of the odorants as videotaped while the infant slept. Direction of initial head turn served as the dependent measure. A significant interaction with Smell x Nostril x Direction was found. Post hoc analyses revealed that significant effects occurred only for the positive smells. When the positive smells were presented to the left hemisphere, neonates made significantly more head turns towards the smell. This raises the possibility that approach behaviours may develop earlier than withdrawal behaviours.

Prenatal experience and neonatal responsiveness to vocal expressions of emotion.

Newborn differentiation of emotion and the relevance of prenatal experience in influencing responsiveness to emotion was tested by examining newborn responses to the presentation of a range of vocal expressions. Differential responding was observed, as indicated by an increase in eye opening behavior in response to the presentation of happy speech patterns. More importantly, differential responding was observed only when the infants listened to emotional speech as spoken by speakers of their maternal language. No evidence of discrimination was found in the groups of infants listening to the same vocal expressions in a novel language. The results suggest that as a consequence of prenatal exposure to the distinctive prosodic maternal speech patterns that specify different emotions and to the temporally related stimuli created by distinctive maternal physiological concomitants of emotion, the fetus learns to differentiate those emotional speech patterns typical of the infant's maternal language.

Asymmetric headturning to speech and nonspeech in human newborns.

Functional asymmetries were examined in 59 newborns by recording headturns from midline to binaurally equivalent sounds. Results showed that robust, asymmetric pattern of headturning occurred in most newborns' responses to binaurally presented unfiltered female speech sounds, with increased rightward orientation demonstrated in five replications. Female speech that was modified by attenuation of frequencies above 500 Hz, as well as speech attenuated below 1500 Hz and above 3000 Hz, resulted in a significant rightward bias in headturning. In contrast, female speech attenuated below 3500 Hz, and continuous, repetitive stimuli such as heartbeat sounds and phrases of speech repeated at the rate of heartbeat (termed heartspeech), failed to generate the rightward orientation bias. These results suggest that female speech sounds, particularly low-frequency sounds related to the naturally occurring prosodic characteristics of speech, are a salient class of stimuli for the organization of lateral biases in orienting in newborns.

Dynamic organization of intersensory function.

Issues related to infant intersensory functioning are reviewed. The argument is offered that limitations of sensory inputs during early stages of development are necessary and provide structure and organization which determine behavioural characteristics at later stages. It is also suggested that infant organisms respond to the intensity of stimulation rather than organizational characteristics and that this is responsible for the form of sensory equivalence apparent during early development. A scheme for the investigation of sources of intersensory organization is presented which involves a prospective analysis of how consideration of the times of onset of sensory functions helps us to understand intra- and intersensory development. The advantages of this experimental approach are outlined.

Shifts in hemispheric advantage during familiarization with complex visual patterns.

Twenty females unfamiliar with kanji were given a recognition task involving tachistoscopic presentation of kanji to the right and left visual fields. Repeated exposure to these novel stimuli resulted in significantly increased competence at the task. To analyze different approaches to the task, subjects were divided into an initial left visual field advantage and an initial right visual field advantage group. Over the course of the experiment subjects in the initial left visual field advantage group shifted from a left to a right visual field advantage, showing both a linear trend and a quadratic trend, while the initial right visual field advantage group showed only a quadratic trend. The results are consistent with observations in other novel stimuli situations which have demonstrated a shift in hemispheric advantage from right to left with increased competence and which have demonstrated individual differences in the pattern of shifting hemispheric advantage.

Auditory-visual equivalence by mentally retarded and intellectually average older children.

Auditory-visual information equivalence in 15 mentally retarded and 15 intellectually average 12- to 13-year-old children were compared using nine matching tasks. Intellectually average subjects were more accurate on both intra- and intersensory tasks. Retarded subjects were more accurate on intra- than on intersensory tasks, whereas there was no such difference for the average subjects. Tasks involving transposition were more difficult for the retarded children than those not involving transposition. The intellectually average children behaved similarly on intrasensory tasks but on intersensory tasks were more accurate when transposition was involved. There was no association between IQ and intra- or intersensory performance when data from the two groups were examined separately.

Effects of unusually early visual stimulation on the development of homing behavior in the rat pup.

Two studies examined the theory that early limitations on sensory functioning contribute to the organization of a structure for perceptual development and intersensory functioning. Rat pups' eyelids were surgically opened on Day 7, following which the development of homing to their nest site was investigated, with each animal alone in its living cage. Control pups increased homing until Day 14, and then decreased. Experimental pups showed no such decline, with the highest rate of homing evident on the last day of testing. The importance of visual cues for this altered development of homing was examined. Visual cues for the home were reduced by removing all shavings during testing, while leaving an odorous substrate in place. Under these conditions, both groups showed the characteristic increase and decline in homing, suggesting that premature eyelid opening results in a modification of the distribution of attention to visual and olfactory characteristics of the nest.

The role of developmental limitations of sensory input on sensory/perceptual organization.

The human infant is born with limited sensory capacities. Such limitations are characteristic of early stages of development of all mammals. These limitations have been conceptualized as equivalent to sensory deprivation, and it has frequently been assumed that compensatory stimulation would therefore be advantageous. It is our contention that, during normal development, limitations provide an organizational framework which enhances perceptual development, and that providing additional stimulation to prematurely born infants may, in fact, be harmful. In addition to reviewing the literature on this issue, we present the results of several studies in which the effect of surgically opening the eyes of rat pups prior to the age of normal eye opening was examined. These studies found alterations in the patterns of homing consequent upon the early availability of visual input. Pups whose eyes were opened early failed to exhibit the transitions in behavior normally found to occur around the time of eye opening. Furthermore, the pups failed to respond differentially to olfactory stimuli which littermate controls successfully discriminated.

Auditory-visual integration by mentally retarded adolescents.

The ability of mildly mentally retarded adolescents to identify the equivalence of auditory and visual stimuli under conditions that did and did not involve transposition from spatial to temporal and vice versa was examined. Subjects' abilities to judge equivalence of stimuli within a modality under conditions that required transposition from spatial patterns to temporal patterns was also examined. They scored significantly better on intra- than on intersensory tasks and had no more difficulty with intrasensory tasks requiring transposition than with tasks requiring no transposition. On intersensory tasks, however, the subjects' performance was significantly worse on tasks requiring transposition.

Relationship between changes in hemispheric advantage during familiarization to faces and proficiency in facial recognition.

Female college students were given a task involving the recognition of initially unfamiliar faces which were tachistoscopically presented to one or the other visual field. Subjects who showed a left visual field advantage made fewer errors than those who showed a right visual field advantage both at the very beginning of the task, when the faces were totally unfamiliar, and at the end of the task, when the faces were relatively familiar; however, during intermediate phases of familiarization, there was no difference in number of errors between subjects with right and left visual field advantages. The results support our previously proposed view that there are shifts in the processing of facial information, beginning with a relatively undifferentiated holistic type of right hemisphere processing, progressing to an analytic mode of left hemisphere processing and culminating in a mode of right hemisphere processing in which distinctive features are incorporated into an articulated whole. The results further suggest that the direction of hemispheric advantage shown at different periods in the course of familiarization is related to level of proficiency.

Changes in visual field advantage for facial recognition: the development of a general processing strategy.

During the recognition of tachistoscopically presented faces, subjects initially showing a LVF advantage decrease and then increase that advantage; subjects with an initial RVF advantage shift to a LVFA. We examined whether these shifts result from increasing familiarity with specific faces or rather from the development of a more general facial processing strategy. This was accomplished by changing the set of faces presented for recognition during testing. Across trials, the VFA of initially RVF advantaged subjects showed a linear trend, that of LVF advantaged S's a quadratic trend. These trends don't differ from those of subjects tested with one set of faces, suggesting that subjects were learning a general strategy for facial recognition.

Changes in hemispheric advantage in processing facial information with increasing stimulus familiarization.

Thirty-nine female subjects were given a task involving recognition of initially unfamiliar faces which were tachistoscopically presented to one or the other visual field. In support of a hypothesized dual mode of right hemisphere function, those subjects who showed an initial left visual field advantage exhibited a diminution and then an increase in this advantage with increasing familiarity with the faces. This resulted in a significant quadratic component in their magnitude of hemispheric advantage. In contrast, those individuals who showed an initial right visual field advantage had neither a significant linear nor quadratic component in the magnitude of their advantage. Significant correlations between number of errors and magnitude of hemispheric advantage, independent of direction, were also found. The results are discussed in terms of possible optimal sequences and timing of shifts in information processing strategies and associated hemispheric advantages.

Limitations on input as a basis for neural organization and perceptual development: a preliminary theoretical statement.

We propose an alternative to the conventional view that limitations on infant functioning are handicaps to be overcome. According to our view, limitations, particularly of the sensory systems, produce adaptive advantages for infants by facilitating perceptual organization. During embryogenesis, developmental rates of sensory systems are unequal so that onset of functioning is sequential. We argue that such differential onset results in relative independence among emerging systems, thereby reducing competition which helps regulate subsequent neurogenesis and functioning. In addition to prenatal effects, neonatal sensory limitations are discussed as a major source of perceptual organization. Limitations reduce the amount of information with which the infant must contend and promote temporal contiguity between multimodal attributes of a stimulus. Although we focus on human perceptual development, our view is a broadly based comparative one. Thus, other organisms have evolved means of restricting sensory input, and evidence is cited suggesting the importance of this reduced input in regulating normal perceptual development.

Intersensory interaction in newborns: modification of visual preferences following exposure to sound.

The present study investigated intersensory interaction between auditory and visual stimulation in newborn infants. Stimulation in 1 modality may influence the response to stimulation in a second modality by changing the infant's state of arousal. To test this possibility, newborns' visual preferences for light patches of different intensity were examined following auditory stimulation. Visual preferences in infants not previously exposed to sound described an inverted U, indicating a preference for the light of intermediate intensity. In contrast, infants who were first exposed to sound preferred the light or lowest intensity. The results indicate that newborns attend to quantitative variations in stimulation and that these variations reflect both the objective stimulus intensity and organismic factors.

Alterations of maternal behaviors of female rats caring for malnourished pups.

The maternal care received by rat pups malnourished by being rotated between lactating females and nonlactating foster mothers was examined. During the 1st 2 weeks after birth there were no differences in maternal care, but during the 3rd week females caring for pups fed only 8 hr daily nursed more and built better nests than females caring for pups fed 16 or 24 hr. These differences in maternal care may interact with and diminish any effects of nutritional deprivation in the pups.

Individual differences in cerebral asymmetries for facial recognition.

In the recognition of tachistoscopically presented unmasked upright faces, some individuals showed a RVF, i.e., left-hemisphere advantage while others showed a LVF, i.e., right-hemisphere advantage. Individuals with a LVF advantage in recognition of these faces showed an increase in errors when the faces were inverted whereas those with a RVF advantage did not. Individuals with a RVF advantage in recognition of the unmasked upright faces showed a greater increase in errors when individual features of the faces were masked than those with a LVF advantage. These results confirmed the view that individuals with a RVF advantage in facial recognition were using an analytic strategy in processing the stimuli whereas those with a LVF advantage were using a holistic strategy.

Sensory influences on homing of stunted rat pups.

The effects of 2 methods of restricting food intake--large-litter rearing and rotation between lactating and nonlactating females--on sensory factors involved in homing to the nest by rat pups were examined. Homing was observed in the unaltered home cage, when olfactory cues were altered and when visual cues were altered. Stunted animals homed less in the unaltered cage than did well-nourished controls as a result of a maturational delay. Prior to eye opening, stunted animals showed greater disruption of homing when olfactory cues were altered and after eye opening they showed greater disruption when visual cues were altered. These effects could reflect decreased sensitivity, an inability to use alternate cues, or behavioral disruption by novel stimulation. Nonnutritional factors were also found to affect homing as the 2 well-nourished groups differed in their behaviors. These differences appeared to be due to animals reared in small litters maturing more slowly than animals rotated between females.

Intersensory function in newborns: effect of sound on visual preferences.

The results of this study indicate that newborn infants' fixation of a graduated series of visual stimuli comprised of a low (1), intermediate (4 or 16), and a high (64) number of cubes is significantly different in the absence and presence of sound (white-noise bursts). Relative to the no-sound condition, sound resulted in the infants' tendency to look more at the low-intensity visual stimulus and less at the high-intensity visual stimulus. These results provide support for the idea that the newborns' optimal or preferred amount of stimulation is based on the total amount or intensity of stimulus input, regardless of whether this is contributed to by stimulation from one or more than one modality.

Development of home orientation in hypothyroid and hyperthyroid rat pups.

In order to assess the effects of perinatal hypothyroidism or hyperthyroidism on the development of an integrated behavioral response, we tested hypothyroid, hyperthyroid, and control pups, as well as pups receiving thyroxine replacement therapy, for the development of the home orientation response. Hypothyroidism was induced in the pups by feeding the pregnant or lactating female a diet of .2% propylthiouracil from Day 15 of gestation to Day 22 postpartum. Pups receiving replacement therapy and pups made hyperthyroid were injected daily with thyroxine, starting at birth. The ability of the pups to initiate and maintain locomotion toward the nest was assessed between Days 4 and 22. Hyperthyroid, control, and replacement therapy pups behaved very similarly on the task, showing a peak in the percentage of pups homing between Days 12 and 16. Hypothyroid pups showed a delay in the peak percentage until Day 20, although the percentage of pups was similar to that found in other treatments. An integrated behavioral response can be delayed by hypothyroidism and still emerge apparently intact at a later age.