Intersensory redundancy facilitates prenatal perceptual learning in bobwhite quail (Colinus virginianus) embryos.

Information presented redundantly and in temporal synchrony across sensory modalities (intersensory redundancy) selectively recruits attention and facilitates perceptual learning in human infants. This comparative study examined whether intersensory redundancy also facilitates perceptual learning prenatally. The authors assessed quail (Colinus virginianus) embryos' ability to learn a maternal call when it was (a) unimodal, (b) concurrent but asynchronous with patterned light, or (c) redundant and synchronous with patterned light. Chicks' preference for the familiar over a novel maternal call was assessed 24 hr following hatching. Chicks receiving redundant, synchronous stimulation as embryos learned the call 4 times faster than those who received unimodal exposure. Chicks who received asynchronous bimodal stimulation showed no evidence of learning. These results provide the first evidence that embryos are sensitive to redundant, bimodal information and that it can facilitate learning during the prenatal period.     

Increasing task difficulty enhances effects of intersensory redundancy: testing a new prediction of the Intersensory Redundancy Hypothesis

Prior research has demonstrated intersensory facilitation for perception of amodal properties of events such as tempo and rhythm in early development, supporting predictions of the Intersensory Redundancy Hypothesis (IRH). Specifically, infants discriminate amodal properties in bimodal, redundant stimulation but not in unimodal, nonredundant stimulation in early development, whereas later in development infants can detect amodal properties in both redundant and nonredundant stimulation. The present study tested a new prediction of the IRH: that effects of intersensory redundancy on attention and perceptual processing are most apparent in tasks of high difficulty relative to the skills of the perceiver. We assessed whether by increasing task difficulty, older infants would revert to patterns of intersensory facilitation shown by younger infants. Results confirmed our prediction and demonstrated that in difficult tempo discrimination tasks, 5‐month‐olds perform like 3‐month‐olds, showing intersensory facilitation for tempo discrimination. In contrast, in tasks of low and moderate difficulty, 5‐month‐olds discriminate tempo changes in both redundant audiovisual and nonredundant unimodal visual stimulation. These findings indicate that intersensory facilitation is most apparent for tasks of relatively high difficulty and may therefore persist across the lifespan.     

The development of infant discrimination of affect in multimodal and unimodal stimulation: The role of intersensory redundancy

This research examined the developmental course of infants' ability to perceive affect in bimodal (audiovisual) and unimodal (auditory and visual) displays of a woman speaking. According to the intersensory redundancy hypothesis (L. E. Bahrick, R. Lickliter, & R. Flom, 2004), detection of amodal properties is facilitated in multimodal stimulation and attenuated in unimodal stimulation. Later in development, however, attention becomes more flexible, and amodal properties can be perceived in both multimodal and unimodal stimulation. The authors tested these predictions by assessing 3-, 4-, 5-, and 7-month-olds' discrimination of affect. Results demonstrated that in bimodal stimulation, discrimination of affect emerged by 4 months and remained stable across age. However, in unimodal stimulation, detection of affect emerged gradually, with sensitivity to auditory stimulation emerging at 5 months and visual stimulation at 7 months. Further temporal synchrony between faces and voices was necessary for younger infants' discrimination of affect. Across development, infants first perceive affect in multimodal stimulation through detecting amodal properties, and later their perception of affect is extended to unimodal auditory and visual stimulation. Implications for social development, including joint attention and social referencing, are considered.     

Infants’ perception of rhythm and tempo in unimodal and multimodal stimulation: A developmental test of the intersensory redundancy hypothesis

Research has demonstrated that young infants can detect a change in the tempo and the rhythm of an event when they experience the event bimodally (audiovisually), but not when they experience it unimodally (acoustically or visually). According to Bahrick and Lickliter (2000, 2002), intersensory redundancy available in bimodal, but not in unimodal, stimulation directs attention to the amodal properties of events in early development. Later in development, as infants become more experienced perceivers, attention becomes more flexible and can be directed toward amodal properties in unimodal and bimodal stimulation. The present study tested this developmental hypothesis by assessing the ability of older, more perceptually experienced infants to discriminate the tempo or rhythm of an event, using procedures identical to those in prior studies. The results indicated that older infants can detect a change in the rhythm and the tempo of an event following both bimodal (audiovisual) and unimodal (visual) stimulation. These results provide further support for the intersensory redundancy hypothesis and are consistent with a pattern of increasing specificity in perceptual development.     

Intersensory redundancy guides attentional selectivity and perceptual learning in infancy

This study assessed an intersensory redundancy hypothesis, which holds that in early infancy information presented redundantly and in temporal synchrony across two sense modalities selectively recruits attention and facilitates perceptual differentiation more effectively than does the same information presented unimodally. Five-month-old infants' sensitivity to the amodal property of rhythm was examined in 3 experiments. Results revealed that habituation to a bimodal (auditory and visual) rhythm resulted in discrimination of a novel rhythm, whereas habituation to the same rhythm presented unimodally (auditory or visual) resulted in no evidence of discrimination. Also, temporal synchrony between the bimodal auditory and visual information was necessary for rhythm discrimination. These findings support an intersensory redundancy hypothesis and provide further evidence for the importance of redundancy for guiding and constraining early perceptual learning.     

Prenatal experience and postnatal perceptual preferences: evidence for attentional-bias in bobwhite quail embryos (Colinus virginianus)

Previous studies have indicated that concurrent multimodal sensory stimulation can interfere with prenatal perceptual learning. This study further examined this issue by exposing 3 groups of bobwhite quail embryos (Colinus virginianus) to (a) no supplemental stimulation, (b) a bobwhite maternal call, or (c) a maternal call paired with a pulsating light in the period prior to hatching. Experiments differed in terms of the types of stimuli presented during postnatal preference tests. Embryos receiving no supplemental stimulation showed no preference between stimulus events in all testing conditions. Embryos receiving exposure to the unimodal maternal call preferred the familiar call over an unfamiliar call regardless of the presence or absence of pulsating light during testing. Embryos exposed to the call-light compound preferred the familiar call only when it was paired with the light during testing. These results suggest that concurrent multimodal stimulation does not interfere with prenatal perceptual learning by overwhelming the young organism's limited attentional capacities. Rather, multimodal stimulation biases what information is attended to during exposure and subsequent testing.     

Modified prenatal sensory stimulation influences postnatal behavioral and perceptual responsiveness in bobwhite quail chicks (Colinus virginianus)

Asynchronous bimodal stimulation during prenatal development elicits higher levels of behavioral and physiological arousal in precocial avian embryos than does unimodal sensory stimulation. To investigate whether the increased arousal associated with prenatal bimodal stimulation has enduring effects into postnatal development, bobwhite quail (Colinus virginianus) embryos received no supplemental stimulation, unimodal auditory stimulation, or bimodal (audiovisual) stimulation prior to hatching. Embryos exposed to concurrent bimodal stimulation demonstrated greater levels of behavioral activity and failed to use maternal visual cues to successfully direct species-specific perceptual preferences following hatching. These results provide initial evidence that asynchronous bimodal sensory stimulation during prenatal development can have enduring effects on early postnatal behavioral arousal and perceptual responsiveness and suggest that developmental limitations on prenatal sensory stimulation play an important role in the emergence of species-typical behavior.     

The role of intersensory redundancy in the emergence of social referencing in 5½-month-old infants

Early evidence of social referencing was examined in 5?-month-old infants. Infants were habituated to 2 films of moving toys, one toy eliciting a woman's positive emotional expression and the other eliciting a negative expression under conditions of bimodal (audiovisual) or unimodal visual (silent) speech. It was predicted that intersensory redundancy provided by audiovisual (but not available in unimodal visual) events would enhance detection of the relation between emotional expressions and the corresponding toy. Consistent with predictions, only infants who received bimodal, audiovisual events detected a change in the affect-object relations, showing increased looking during a switch test in which the toy-affect pairing was reversed. Moreover, in a subsequent live preference test, they preferentially touched the 3-dimensional toy previously paired with the positive expression. These findings suggest social referencing emerges by 5? months in the context of intersensory redundancy provided by dynamic multimodal stimulation and that even 5?-month-old infants demonstrate preferences for 3-dimensional objects on the basis of affective information depicted in videotaped events.     

Early visual experience affects postnatal auditory responsiveness in bobwhite quail (Colinus virginianus)

Results from 6 experiments suggest perinatal visual experience interferes with postnatal auditory responsiveness in bobwhite quail (Colinus virginianus). Light- or dark-reared control chicks responded similarly to bobwhite maternal Calls A or B following hatching. Light-reared chicks that experienced 10 min/hr of Call A or B from hatching until testing preferred the familiar call at Days 2-4, but dark-reared chicks preferred the familiar call at all ages. Increased amounts of exposure to maternal calls during postnatal Days 1-2 led to auditory responsiveness deficits in light-reared chicks. Similarly, embryos exposed to 10 min/hr of prenatal visual cues required 48 hr of postnatal Call A or B exposure to demonstrate auditory discrimination. These findings highlight the linkages between developing auditory and visual systems during infancy.     

Intersensory redundancy promotes visual rhythm discrimination in visually impaired infants

Infants’ attention is captured by the redundancy of amodal stimulation in multimodal objects and events. Evidence from this study demonstrates that intersensory redundancy can facilitate discrimination of rhythm changes presented in the visual modality alone in visually impaired infants, suggesting that multisensory rehabilitation strategies could prove helpful in this population.     

Interactive and vicarious acquisition of auditory preferences in Northern bobwhite (Colinus virginianus) chicks

Studies examining the effects of stimulus contingency on filial imprinting have produced inconsistent findings. In the current study, day-old bobwhite chicks (Colinus virginianus) received individual 5-min sessions in which they were provided contingent, noncontingent, or vicarious exposure to a variant of a bobwhite maternal assembly call. Chicks given contingent exposure to the call showed a significant preference for the familiar call 24 hr following exposure and significantly greater preferences than chicks given noncontingent exposure. Chicks given vicarious exposure to recordings of another chick interacting with the maternal call showed significant deviations from chance responding; however, the direction of chick preference (toward the familiar or unfamiliar) depended on the particular call used. These results indicate that both direct and indirect (vicarious) exposure to stimulus contingency can enhance the acquisition of auditory preferences in precocial avian hatchlings. Precocial avian hatchlings thus likely play a more active role in directing their own perceptual and behavioral development than has typically been thought.     

Development of species identification in ducklings: II. Experimental prevention of perceptual deficit caused by embryonic auditory deprivation.

Devocalized-isolated ducklings are relatively insensitive to the higher frequencies in their species' maternal call 24 hr after hatching. To assess the efficacy of various sounds in preventing this high-frequency perceptual deficit, devocalized-isolated embryos were exposed to one of three calls and tested with normal versus high-frequency attenuated maternal calls 24 hr after hatching. The embryonic vocalization (contact-contentment call) that most closely matched the region of the devocalized ducklings' greatest insensitivity (1,500-2,500 Hz) proved most efficacious in remedying (preventing) the high-frequency perceptual deficit. Exposure to the embryonic alarm-distress call was somewhat effective, whereas exposure to low-frequency white noise was not effective at all. This finding suggests that the normal development of innate behavior is partially dependent upon prior experience as well as upon intrinsic processes of neural maturation. Although normally occurring embryonic auditory experience does not induce the preference for the maternal call in this species, such experience does contribute to the sharpness of the discriminative basis of the preference 24 hr after hatching.     

Development of species identification in ducklings: III. Maturational rectification of perceptual deficit caused by auditory deprivation.

Mute ducklings, devocalized as embryos and maintained in auditory isolation, manifest a selective high-frequency perceptual deficit vis-à-vis the maternal call of their species at 24 hr after hatching. Since it takes a rather specific auditory experiential input to rectify this high-frequency insensitivity at 24 hr, it was predicted that, in the absence of auditory experience, devocal-isolated ducklings would fail to show sufficient endogenously mediated improvement to bring them up to the level of perceptual competence of vocal-communal ducklings at any age. This hypothesis proved wrong in that the proportion of devocalized ducklings showing a preference for the normal maternal call over the greater than 825-Hz attenuated one became equivalent to the vocal ducklings at 48 hr after hatching, as did their ability to discriminate the normal maternal call from greater than 1,800-Hz attenuated maternal call. At 65 hr, however, the devocalized ducklings' performance deteriorated back to the level observed at 24 hr. Embryonic exposure to the (sibling) contact-contentment call prevents the perceptual deficit at 24 hr and the deterioration at 65 hr.     

Constrained motor-perceptual task in infancy: effects of sensory modality

The authors examined the relative success of varying sensory stimulation modalities that they presented via a mobile reinforcement procedure for promoting left-knee extensions in 3-month-old infants. They separated 53 infants into 5 groups. Four groups received contingent unimodal auditory, enhanced auditory, or visual reinforcement or contingent bimodal auditory plus visual (aud + vis) reinforcement. One group (controls) received aud + vis noncontingent reinforcement. The group that received aud + vis contingent reinforcement was most successful in learning the motor task and maintained the highest attention levels. The authors observed few differences in learning and attention within the unimodal groups. The present findings confirm the effectiveness of contingent multisensory stimulation for promoting perception-action coupling in infancy.     

Redundant amodal properties facilitate operant learning in 3-month-old infants

The current study examined the role redundant amodal properties play in an operant learning task in 3-month-old human infants. Prior studies have suggested that the presence of redundant amodal information facilitates detection and discrimination of amodal properties and potentially functions to influence general learning processes such as associative conditioning. The current study examined how human infants use redundant amodal information (visual and haptic) about the shape of an object to influence learning of an operant response. Infants learned to kick to move a mobile of cylinders while either holding a cylinder, a rectangular cube, or no object. Kick rate served as the dependent measure. The results showed that infants given matching redundant amodal properties (e.g., viewed cylinders while holding a cylinder) showed facilitated operant learning whereas infants given mismatching redundant amodal properties showed inhibited operant learning. These results support and extend the Intersensory Redundancy Hypothesis by demonstrating that amodal redundancy influences complex learning processes such as operant conditioning.     

Intermodal perception at birth: Intersensory redundancy guides newborn infants’ learning of arbitrary auditory−visual pairings

In this study the ability of newborn infants to learn arbitrary auditory–visual associations in the absence versus presence of amodal (redundant) and contingent information was investigated. In the auditory-noncontingent condition 2-day-old infants were familiarized to two alternating visual stimuli (differing in colour and orientation), each accompanied by its ‘own’ sound: when the visual stimulus was presented the sound was continuously presented, independently of whether the infant looked at the visual stimulus. In the auditory-contingent condition the auditory stimulus was presented only when the infant looked at the visual stimulus: thus, presentation of the sound was contingent upon infant looking. On the post-familiarization test trials attention recovered strongly to a novel auditory–visual combination in the auditory-contingent condition, but remained low, and indistinguishable from attention to the familiar combination, in the auditory-noncontingent condition. These findings are a clear demonstration that newborn infants’ learning of arbitrary auditory–visual associations is constrained and guided by the presence of redundant (amodal) contingent information. The findings give strong support to Bahrick’s theory of early intermodal perception.     

Exploring early developmental changes in face scanning patterns during the perception of audiovisual mismatch of speech cues

Young infants are capable of integrating auditory and visual information and their speech perception can be influenced by visual cues, while 5-month-olds detect mismatch between mouth articulations and speech sounds. From 6 months of age, infants gradually shift their attention away from eyes and towards the mouth in articulating faces, potentially to benefit from intersensory redundancy of audiovisual (AV) cues. Using eye tracking, we investigated whether 6- to 9-month-olds showed a similar age-related increase of looking to the mouth, while observing congruent and/or redundant versus mismatched and non-redundant speech cues. Participants distinguished between congruent and incongruent AV cues as reflected by the amount of looking to the mouth. They showed an age-related increase in attention to the mouth, but only for non-redundant, mismatched AV speech cues. Our results highlight the role of intersensory redundancy and audiovisual mismatch mechanisms in facilitating the development of speech processing in infants under 12 months of age.     

Modification of prenatal auditory experience alters postnatal auditory preferences of bobwhite quail chicks.

This study assessed the effects of altered prenatal auditory experience on bobwhite quail chicks' (Colinus virginianus) species-specific preference for the bobwhite maternal call. Results revealed that when the repetition rate of the embryonic vocalizations normally present in the prenatal environment was altered, the species-typical auditory preference of hatchlings for the maternal call was also altered. Specifically, embryos exposed to embryonic vocalizations with a faster repetition rate than normal subsequently preferred a bobwhite maternal call with a faster repetition rate over one with its normal repetition rate. Bobwhite embryos thus appear able to abstract features of their prenatal auditory environment to other auditory events in the postnatal period. This demonstration of prenatal perceptual learning is in keeping with other recent studies from behavioural embryology, which have also demonstrated that prenatal perceptual experience can influence later responses to species-typical stimulation.     

Multisensory processing in the redundant-target effect: a behavioral and event-related potential study

Participants respond more quickly to two simultaneously presented target stimuli of two different modalities (redundant targets) than would be predicted from their reaction times to the unimodal targets. To examine the neural correlates of this redundant-target effect, event-related potentials (ERPs) were recorded to auditory, visual, and bimodal standard and target stimuli presented at two locations (left and right of central fixation). Bimodal stimuli were combinations of two standards, two targets, or a standard and a target, presented either from the same or from different locations. Responses generally were faster for bimodal stimuli than for unimodal stimuli and were faster for spatially congruent than for spatially incongruent bimodal events. ERPs to spatially congruent and spatially incongruent bimodal stimuli started to differ over the parietal cortex as early as 160 msec after stimulus onset. The present study suggests that hearing and seeing interact at sensory-processing stages by matching spatial information across modalities.     

Bimodal and trimodal multisensory enhancement: effects of stimulus onset and intensity on reaction time

Manual reaction times to visual, auditory, and tactile stimuli presented simultaneously, or with a delay, were measured to test for multisensory interaction effects in a simple detection task with redundant signals. Responses to trimodal stimulus combinations were faster than those to bimodal combinations, which in turn were faster than reactions to unimodal stimuli. Response enhancement increased with decreasing auditory and tactile stimulus intensity and was a U-shaped function of stimulus onset asynchrony. Distribution inequality tests indicated that the multisensory interaction effects were larger than predicted by separate activation models, including the difference between bimodal and trimodal response facilitation. The results are discussed with respect to previous findings in a focused attention task and are compared with multisensory integration rules observed in bimodal and trimodal superior colliculus neurons in the cat and monkey.