The infant vocal-conditioning literature: a theoretical and methodological critique

Most studies of operant conditioning of infant vocalization do not fully use the experimental-analysis-of-behavior methodology that behavioral researchers have developed to study operant phenomena. This could be a contributing factor in their failure to correctly operationalize the definition of reinforcement, severely limiting the amount of information they can provide about operant learning in infants. Furthermore, single-subject-design studies may be added to supplement or replace group experimental designs in the study of infant vocal conditioning if we are to recognize the different learning processes that affect infant learning. Finally, single-subject experimental designs may be crucial to the development of an effective technology of early language intervention.     

Developmental changes in associations between auditory-visual events

The goal of the present study was twofold: to examine the influence of two amodal properties, co-location and temporal synchrony, on infants' associating a sight with a sound, and to determine if the relative influence of these properties on crossmodal learning changes with age. During familiarization 2-, 4-, 6- and 8-month-olds were presented two toys and a sound, with sights and sounds varying with respect to co-location and temporal synchrony. Following each familiarization phase infants were given a paired preference test to assess their learning of sight-sound associations. Measures of preferential looking revealed age-related changes in the influence of co-location and temporal synchrony on infants' learning sight-sound associations. At all ages, infants could use temporal synchrony and co-location as a basis for associating an auditory with a visual event and, in the absence of temporal synchrony, co-location was sufficient to support crossmodal learning. However, when these cues conflicted there were developmental changes in the influence of these cues on infants' learning auditory-visual associations. At 2 and 4 months infants associated the sounds with the toy that moved in synchrony with the sound's rhythm despite extreme violation of co-location of this sight and sound. In contrast, 6- and 8-month-olds did not associate a specific toy with the sound when co-location and synchrony information conflicted. The findings highlight the unique and interactive effects of distinct amodal properties on infants' learning arbitrary crossmodal relations. Possible explanations for the age shift in performance are discussed.     

Visual cognition influences early vision: the role of visual short-term memory in amodal completion

A partly occluded visual object is perceptually filled in behind the occluding surface, a process known as amodal completion or visual interpolation. Previous research focused on the image-based properties that lead to amodal completion. In the present experiments, we examined the role of a higher-level visual process-visual short-term memory (VSTM)-in amodal completion. We measured the degree of amodal completion by asking participants to perform an object-based attention task on occluded objects while maintaining either zero or four items in visual working memory. When no items were stored in VSTM, participants completed the occluded objects; when four items were stored in VSTM, amodal completion was halted (Experiment 1). These results were not caused by the influence of VSTM on object-based attention per se (Experiment 2) or by the specific location of to-be-remembered items (Experiment 3). Items held in VSTM interfere with amodal completion, which suggests that amodal completion may not be an informationally encapsulated process, but rather can be affected by high-level visual processes.     

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.     

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.     

Identification of a reinforcement pathway necessary for operant conditioning of head waving in Aplysia californica

The marine mollusc Aplysia californica exhibits a wide range of nonassociative and associative forms of learning. Recently, we found that the learning repertoire of Aplysia includes operant conditioning (Cook & Carew, 1986, 1989b). The behavior we examined is a naturally occurring, side-to-side head-waving response used by Aplysia in seeking food, obtaining a foothold, and egg laying. Aplysia can be operantly conditioned to reduce head-waving to one side of their body if such a response results in exposure to bright uniform-field illumination, which the animals find aversive. An essential step toward achieving a mechanistic understanding of operant conditioning is to identify and characterize the reinforcement pathway used during the learning. Toward this end, we wished to determine which of the peripheral visual pathways in Aplysia are critical for performance of the operant task. Previous experiments indicated that photic input from the optic and rhinophore nerves functionally inhibited motor neurons that participate in the operant response (head-waving), while photic input from the oral veil nerves excited these same motor neurons (Cook & Carew, 1989c). These findings suggested the hypothesis that one or both of these pathways could play an important role in mediating reinforcement during training. To explore this possibility we operantly trained animals that had received chronic bilateral transections of either the optic and rhinophore nerves or the oral veil nerves C1-C3 (in conjunction with transection of the optic and rhinophore nerves). We found that operant conditioning was not disrupted by ablation of input from the eyes and rhinophores. By contrast, ablation of input from the oral veil (together with that from the eyes and rhinophores) abolished operant conditioning. Thus, the oral veil nerves play a critical modulatory role in operant conditioning of head-waving. This observation further suggested that photic input from the oral veil is conveyed to the CNS via the oral veil nerves. In a final experiment we confirmed that stimulation of the oral veil with light evokes increased afferent activity in the oral veil nerves C1-C2. These results support the idea that the oral veil nerves contain processes that are critical components of the reinforcement pathway for operant conditioning of head-waving.     

Development of modal and amodal completion in infants

Visual completion has been divided into two types: modal and amodal. While psychophysical studies with adults provided several common properties between modal and amodal completion, studies with infants showed differential trends in the development of these perceptual abilities. In the present study, we further examined the development of these two kinds of visual completion in infants aged 3 to 6 months. We created a display composed of a partially overlapping circle and square. The display induced either modal or amodal completion depending on the colour. Infants were familiarised with either the modal or the amodal display. After this familiarisation, the infants were tested on their discrimination between the complete figure and the broken figure. If the infants could perceptually complete the figures in the familiarisation display, they were expected to show a novelty preference for the broken figure. A total of thirty-two infants participated in the present study. Our results suggest that modal completion develops by 3-4 months of age, whereas amodal completion develops by 5-6 months of age.     

Intersensory redundancy educates selective attention in bobwhite quail embryos

We assessed whether exposure to amodal properties in bimodal stimulation (e.g. rhythm, rate, duration) could educate attention to amodal properties in subsequent unimodal stimulation during prenatal development. Bobwhite quail embryos were exposed to an individual bobwhite maternal call under several experimental and control conditions during the day prior to hatching. Experimental groups received redundant auditory and visual exposure to the temporal features of an individual maternal call followed by unimodal auditory exposure to the same call immediately or after a 2-hr or 4-hr delay. Control groups received (1) the same exposure but in the reverse sequence (unimodal --> redundant bimodal), (2) asynchronous bimodal --> unimodal, (3) only unimodal exposure, or (4) only bimodal exposure. All experimental groups showed a significant preference for the familiar maternal call over a novel maternal call when tested 2 days after hatching, whereas none of the control groups showed a significant preference for the familiar call. These results indicate that intersensory redundancy can direct attention to amodal properties in bimodal stimulation and educate attention to the same amodal properties in subsequent unimodal stimulation where no intersensory redundancy is available.     

Infants’ emotional states influence maternal behaviors during holding

Previous studies have mainly examined how maternal behaviors influence infants during holding. However it is unclear how infants influence maternal holding. This current study investigated how infants’ emotional states influence maternal holding behaviors, and whether maternal holding behaviors are also influenced by the mothers’ parenting stress. We manipulated infants’ emotional states and videotaped mothers’ holding behaviors. The mothers also completed a questionnaire about their parental stress. Results showed that mothers varied their holding behaviors depending on their infants’ emotional states. When infants were comfortable, mothers rocked them horizontally and quietly. When infants were uncomfortable, mothers rocked them vertically at a high frequency. Furthermore, some types of parenting stress were related to several types of maternal behaviors in the context of holding. These findings suggest that maternal holding behaviors are influenced by both the infants’ emotional states and the mothers’ parenting stress.     

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.     

Extending in vitro conditioning in Aplysia to analyze operant and classical processes in the same preparation

Operant and classical conditioning are major processes shaping behavioral responses in all animals. Although the understanding of the mechanisms of classical conditioning has expanded significantly, the understanding of the mechanisms of operant conditioning is more limited. Recent developments in Aplysia are helping to narrow the gap in the level of understanding between operant and classical conditioning, and have raised the possibility of studying the neuronal processes underlying the interaction of operant and classical components in a relatively complex learning task. In the present study, we describe a first step toward realizing this goal, by developing a single in vitro preparation in which both operant and classical conditioning can be studied concurrently. The new paradigm reproduced previously published results, even under more conservative and homogenous selection criteria and tonic stimulation regime. Moreover, the observed learning was resistant to delay, shortening, and signaling of reinforcement.     

A category-overshadowing effect in pigeons: support for the Common Elements Model of object categorization learning

A model proposing error-driven learning of associations between representations of stimulus properties and responses can account for many findings in the literature on object categorization by nonhuman animals. Furthermore, the model generates predictions that have been confirmed in both pigeons and people, suggesting that these learning processes are widespread across distantly related species. The present work reports evidence of a category-overshadowing effect in pigeons' categorization of natural objects, a novel behavioral phenomenon predicted by the model. Object categorization learning was impaired when a second category of objects provided redundant information about correct responses. The same impairment was not observed when single objects provided redundant information, but the category to which they belonged was uninformative, suggesting that this effect is different from simple overshadowing, arising from competition among stimulus categories rather than individual stimuli during learning.     

Visual discrimination in an orangutan (Pongo pygmaeus): measuring visual preference

Although previous studies have confirmed that trained orangutans visually discriminate between mammals and artificial objects, whether orangutans without operant conditioning can discriminate remains unknown. The visual discrimination ability in an orangutan (Pongo pygmaeus) with no experience in operant learning was examined using measures of visual preference. Sixteen color photographs of inanimate objects and of mammals with four legs were randomly presented to an orangutan. The results showed that the mean looking time at photographs of mammals with four legs was longer than that for inanimate objects, suggesting that the orangutan discriminated mammals with four legs from inanimate objects. The results implied that orangutans who have not experienced operant conditioning may possess the ability to discriminate visually.     

Psychological reactivity to discrepant events: Support for the curvilinear hypothesis

80 male and 60 female infants were observed under 5 a priori judged levels of discrepancy to assess whether sustained attention was linearly or curvilinearly related to degree of discrepancy from an experimental standard. Following habituation, $\text{7}\text{1}\text{2}$-month-old infants were exposed to either the repetition of the standard, a minimal, first- or second-level moderate discrepancy, or a novel stimulus having no relation to the standard. The related stimuli, varying in elongation, were sphere, pear, club, and cylinder-shaped objects; the novel stimulus was a different colored, tooth-like object. 80 infants observed the sphere as the standard and the cylinder as the second-level moderate discrepancy; 60 infants were exposed to the reverse order with the cylinder as the standard. The use of different stimuli at each discrepancy level controlled for specific stimulus effects. Habituation and recovery of responding were observed in an operant paradigm. Lever pressing, fixation, and vocalization increased most to the second-level moderate stimuli and decreased most to the familiar and novel objects; fretting was highest to the redundant stimuli and lowest to the moderate objects. There were no stimulus main effects or interactions. The results support the hypothesis of a curvilinear relation between stimulus discrepancy and sustained attention, excitement, and preference.     

Verbal behavior

The recent history and current status of the area of verbal behavior are considered in terms of three major thematic lines: the operant conditioning of adult verbal behavior, learning to be an effective speaker and listener, and developments directly related to Skinner's Verbal Behavior. Other topics not directly related to the main themes are also considered: the work of Kurt Salzinger, ape-language research, and human operant research related to rule-governed behavior.     

Visual Cues Generated During Action Facilitate 14-Month-Old Infants’ Mental Rotation

Although action experience has been shown to enhance the development of spatial cognition, the mechanism underlying the effects of action is still unclear. The present research examined the role of visual cues generated during action in promoting infants’ mental rotation. We sought to clarify the underlying mechanism by decoupling different aspects of action experience and choosing to manipulate the visual aspect while holding other aspects constant. Fourteen-month-old infants were given opportunities to rotate a cylinder placed on a turntable; the cylinder was decorated with vertical or horizontal stripes. If the effects of action hinge on the quality of visual cues generated during action, infants should benefit more from rotating the cylinder with vertical stripes as they generate richer cues when each stripe moves laterally with the cylinder. As predicted, the infants in the vertical-stripe condition looked significantly longer at an improbable outcome than at a probable outcome of a hidden-rotation event, whereas those in the horizontal-stripe condition looked about equally at the 2 outcomes. The results suggest that the effects of action on mental rotation are derived not from motor experience alone, but from integrating motor and visual experiences.     

Learning blossoms: Caregiver-infant interactions in an outdoor garden setting

Plants provide unique opportunities for learning by engaging all human senses. Recent laboratory studies have shown that infants use a combination of behavioural avoidance and social learning strategies to safely learn about plant properties from adults. Here we investigate how infants and their caregivers interact with plants in an outdoor garden as a first step towards examining the operation of these social learning processes in naturalistic settings. We focus on two specific aspects of spontaneous infant-caregiver interactions with plants: olfactory and touch behaviours. Additionally, we look at whether infants' and caregivers’ prior knowledge of the plants in our study influences infants’ behaviour. Our results showed a multifaceted connection between infants’ and caregivers' previous experience with the plants and their olfactory and touch behaviours. First, infants tended to touch and smell the plants after their caregivers did, and this appeared to be independent of whether infants had seen the plant before. Second, infants systematically engaged in some of the same types of olfactory and touch behaviours their caregiver displayed towards plants. Finally, infants whose caregivers were given more information about the plants in the study showed fewer touch behaviours, but no difference in olfactory behaviours. These findings bolster the previous laboratory studies of plant learning early in life, highlighting the importance of olfactory behaviours, and underscoring the benefits of using ecological observations to explore unique aspects of human development.     

The operant and the classical in conditioned orientation of Drosophila melanogaster at the flight simulator

Ever since learning and memory have been studied experimentally, the relationship between operant and classical conditioning has been controversial. Operant conditioning is any form of conditioning that essentially depends on the animal's behavior. It relies on operant behavior. A motor output is called operant if it controls a sensory variable. The Drosophila flight simulator, in which the relevant behavior is a single motor variable (yaw torque), fully separates the operant and classical components of a complex conditioning task. In this paradigm a tethered fly learns, operantly or classically, to prefer and avoid certain flight orientations in relation to the surrounding panorama. Yaw torque is recorded and, in the operant mode, controls the panorama. Using a yoked control, we show that classical pattern learning necessitates more extensive training than operant pattern learning. We compare in detail the microstructure of yaw torque after classical and operant training but find no evidence for acquired behavioral traits after operant conditioning that might explain this difference. We therefore conclude that the operant behavior has a facilitating effect on the classical training. In addition, we show that an operantly learned stimulus is successfully transferred from the behavior of the training to a different behavior. This result unequivocally demonstrates that during operant conditioning classical associations can be formed.     

Volume completion in 4.5-month-old infants

In this study, we examined 4.5-month-old infants' visual completion of self-occluding three-dimensional objects. A previous study on this topic reported that 6-month-old, but not 4-month-old infants extrapolate a convex, symmetric prism from a limited view of its surfaces (Soska & Johnson, 2008). As of yet, studies on the development of amodal completion of three-dimensional, self-occluding objects are scarce. Given 4-month-old infants' abilities to derive three-dimensional shape from a variety of visual cues, three-dimensional amodal completion may well depend on the perceptual strength of three-dimensionality in the stimulus displays. The first experiments (1A and 1B) tested this hypothesis by means of a habituation paradigm and showed that 4.5-month-old infants are indeed able to amodally complete the back of a self-occluding object when sufficient three-dimensional cues are available. Further support for volume completion in 4.5-month-old infants was found in a second experiment, again using a habituation paradigm, that measured perceived connectedness between two visually separated, self-occluding, three-dimensional objects.     

The four free-operant freedoms

This article reviews early free-operant conditioning laboratory research and applications. The seldom-mentioned four free-operant freedoms are described for the first time in detail. Most current behavior analysts do not realize that the freedom to form responses and the freedom to speed responses were crucial steps in designing free-operant operanda in the 1950s. These four freedoms were known by the laboratory researchers of the 1950s to the point that, along with operanda design, Sidman (1960) did not feel the need to detail them in his classic, Tactics of Scientific Research. The dimensions of freedom in the operant were so well understood and accepted in the 1950s that most thought it redundant to use the term free operant. These issues are reviewed in some detail for younger behavior analysts who did not have the opportunity of learning them firsthand.