Reducing stimulus overselectivity in autistic children

It has been repeatedly reported that when presented with a discrimination task involving multiple cues, autistic children, as compared to normal children, tend to respond on the basis of only a restricted portion of the component cues. This phenomenon has been called stimulus overselectivity and has been implicated as a possible basis for some of the pronounced behavioral deficits characteristic of autism. Examination of the results of several previous studies suggests that the overselectivity effect might be reduced with repeated exposure to testing. However, since the previous studies were not designed to test this hypothesis, no conclusions were drawn regarding variables influencing the reduction of the overselectivity phenomenon. The present investigation was therefore conducted to determine if stimulus overselectivity in autistic children is changed as a function of repeated exposure to testing. Nineteen autistic children were trained on a discrimination task with a cue complex composed of two visual cues. After the children reached criterion on the task, they were exposed to a testing phase with probe trials where the cue components were presented singly. The results indicated that 16 of the children initially showed overselectivity and 3 responded to both cues. Of the 16 children who showed overselectivity, 13 decreased their level of overselectivity with continued testing. These results are discussed in relation to variables in the testing procedure itself and to the literature on selective attention.This research was funded by USPHS Research Grants MH11440, MH28210, and MH28231 from the National Institute of Mental Health. The authors wish to acknowledge the assistance of Cathy Hook, Hannelore Wilhelm, and Jon Killion in conducting this research.     

Stimulus factors in the training of prepositional usage in three autistic children

Language deficient, autistic children were trained to use the prepositions "in" and "on". Three subjects were exposed to conditions of training that differed in the method of employment of stimulus objects used to train prepositional usage. Two subjects were trained first with "ambiguous" stimuli, that is, the same stimulus objects were used for training both prepositions. The two subjects were then switched to a training condition with "non-ambiguous" stimulus objects, that is, objects used for training "in" were different than those used for training "on". The two subjects were then switched to the ambiguous stimulus condition and finally returned again to training with non-ambiguous stimuli (four conditions). A third subject began with training on non-ambiguous stimuli, was switched to an ambiguous condition and was then switched back to non-ambiguous stimuli (three conditions). The results for two of the three subjects indicated that accurate usage of the two prepositions was obtained only under training conditions with non-ambiguous stimuli. Results for the third subject suggested that initial training with non-ambiguous stimuli might enhance subsequent accurate responding with ambiguous stimuli.     

Stimulus duration as a measure of stimulus generalization

Four pigeons in the line-positive group were trained with a vertical line on a green background that signalled intermittent reinforcement while a plain green field signalled extinction. Four pigeons in the line-negative group were trained with the opposite discrimination. Response to a control key terminated any trial and initiated the next trial. The birds also used the control key during generalization tests to control the durations of trials in which various line orientations were presented. These durations were summed to provide generalization gradients of stimulus duration that were positive or negative in accordance with the trained discriminations. In Experiment 2, birds from the line-positive group were tested with a procedure in which the control key was not available on some trials. This provided an independent assessment of response rates to the test stimuli. These rates were used to predict the stimulus durations obtained when the control key was available. The findings supported a general model for the prediction of response distributions among concurrent stimuli from rates observed with single stimuli.     

Stimulus generalization as a function of stimulus novelty and familiarity in rats

Three experiments used rats as subjects to investigate the generalization of conditioned responding between stimuli as a function of the subjects' exposure to these cues prior to conditioning. Experiment 1 used a between-subjects design, food as the reinforcer, and measured the tendency of subjects to approach the site of food delivery during the stimuli. Generalization of this response was more marked when the training and test stimuli were equated in terms of their novelty (i.e., when both were novel or both were familiar) than when the stimuli differed in this respect (i.e., when one was novel and the other was familiar). Experiments 2a and 2b used within-subjects designs to confirm the reliability of the results of Experiment 1. Implications of these results for current theories of stimulus representation are discussed.     

Stimulus learning versus response learning in a discriminated punishment situation

The suppression of bar pressing under two kinds of conditions was compared. Under one condition the response was occasionally punished by shock in the presence of a signal. Suppression to the signal was quickly acquired, indicating rapid learning about the signal-shock relationship (stimulus learning). Under the other condition the response was occasionally punished in the presence of the signal but additional free shocks were given in the absence of the signal. The slow acquisition of suppression found in this case indicated that there was, at best, only gradual learning about the response-shock relationship (response learning).     

Stimulus selection and the number of stimulus components

The number of word components in the compound stimuli of paired-associate lists were varied, and the words within a compound were presented either in a constant or in a variable order from trial to trial. The number of components, above one, had no appreciable effect on the difficulty of learning, and the variable order lists were more difficult than the constant order. Recall with the word components as cues showed that the amount of selection decreased with the variable order lists as the number of components increased. With the constant order lists, selection tended to remain constant as number of components increased. This was interpreted as the result of the availability of a rule for selection in the constant order conditions.     

Eye movements and a dynamic stimulus situation

Two experiments were conducted to investigate performance with and without voluntary eye movements in a dynamic stimulus situation. Experiment I used a combined tracking and prediction task. Level of training, complexity of the signal, and visual region sampled were the variables of interest. Experiment II manipulated the same variables in only the prediction task. Thus, the amount of attention allotted to the prediction task was varied between experiments. The d' measure indicated that under peripheral vision instructions accuracy on the prediction task was the same as under foveal vision instructions provided that: (1) the level of task complexity was low, (2) the subjects were well trained, and (3) only the prediction task was performed, or in the dual task situation only visual regions near the fovea were sampled. All other combinations of the variables resulted in a lower performance scores under peripheral vision instructions. Results are interpreted within the framework of current theories of the functional visual field.     

Stimulus information and stimulus interference in bisensory short-term memory

An attempt was made to determine if Ss’ strategy of retaining stimulus material changed under conditions of bisensory simultaneous stimulation when one of the two inputs was relevant information as opposed to interference. Thus in Group 1 Ss were stimulated bisensorily, attended to both inputs (information), but recalled only one input. Ss in Group 2 were stimulated bisensorily, attended to only one input, and recalled only that input (interference). It was found that S’s efficiency of recall was decreased in the information condition (Group 1) but strategy was not altered. In both groups, Ss performed similarly; performance was in turn similar to that observed in the typical bisensory situation, i.e., where both channels are recalled.     

Auditory overselectivity in autistic children

Autistic and normal children were trained to respond to a complex stimulus containing two auditory components. After the discrimination was acquired, the individual components were presented separately, allowing assessment of the extent to which the child's responding was controlled by one or both of the cues. The autistic children, unlike the normal children, provided evidence for stimulus overselectivity in that 6 of 8 autistic subjects responded to only one of the components. These results are consistent with those of previous studies which showed that when autistic children are presented with a complex visual or multiple-modality stimulus, they selectively respond to only one component of the complex. The present results extend the stimulus overselectivity hypothesis to the situation where all of the stimuli occur within the auditory modality. It is suggested that auditory overselectivity may partially account for autistic deficits in speech comprehension.     

Stimulus presentation versus stimulus removal in the Good Behavior Game

The Good Behavior Game (GBG) is an effective intervention to reduce disruptive behavior. The GBG typically involves immediate stimulus presentation (e.g.., delivery of a token) following disruptions; however, experimenters have also removed tokens contingent upon disruptions. In the present study, we compared the effects of the GBG-stimulus presentation (P) and GBG-stimulus removal (R) on levels of disruptions in a 2nd-grade general education classroom. In addition, we measured student prompts, teacher praise and correctives, and student and teacher preference. The GBG-P and GBG-R versions of the game were similarly effective in reducing disruptions. However, the teacher chose to implement the GBG-R and the majority of students reported a preference for the GBG-R.     

Comparisons of stimulus learning and response learning in a punishment situation

These experiments use a procedure in which a rat is trained to make two topographically distinct responses on a single manipulandum, and then one of the responses is punished. Differential suppression of the punished response is taken as evidence of response learning, whereas the common suppression of both responses is attributed to stimulus learning or to general and nonassociative factors. Thus, this procedure begins the experimental separation of animals learning about the consequences of their behavior and animals learning what happens in a particular environment. A further separation is effected by using two such manipulanda; this procedure begins to distinguish between stimulus learning about the manipulandum and the more gereral factors that cause suppression. Some parameters affecting the relative importance of stimulus learning and response learning are examined.     

Favourite objects of autistic children

Favourite objects (FOs) of autistic children were compared with the FOs of healthy preschool and school children as well as mentally handicapped children. Three clusters of objects were obtained for normal children (comprising primary transitional objects and their forerunners, secondary transitional objects, and non-cuddly toys). When autistic children and mentally handicapped children were included, a fourth cluster of deviant objects was found. Frequency distributions of the two handicapped groups in the clusters were similar. Similarities between the two handicapped groups were also found within each cluster. The occurrence of secondary transitional objects was rare in the handicapped groups. The characteristics of "autistic" FOs reported in earlier case studies (e.g. being hard, often having an exciting effect, not being used in their adequate functions) were typical only of objects in the fourth cluster.     

Stimulus control and compounding with ambient odor as a discriminative stimulus on a free-operant baseline

Previous experiments have demonstrated that the simultaneous presentation of independently established discriminative stimuli can control rates of operant responding substantially higher than the rates occasioned by the individual stimuli. This "additive summation" phenomenon has been shown with a variety of different reinforcers (e.g., food, water, shock avoidance, cocaine, and heroin). Discriminative stimuli previously used in such studies have been limited to the visual and auditory sensory modalities. The present experiment sought to (1) establish stimulus control on a free-operant baseline with an ambient olfactory discriminative stimulus, (2) compare olfactory control to that produced with an auditory discriminative stimulus, and (3) determine whether compounding independently established olfactory and auditory discriminative stimuli produces additive summation. Rats lever pressed for food on a variable-interval schedule in the presence of either a tone or an odor, with comparable control developed to each stimulus. In the absence of these stimuli responding was not reinforced. During stimulus compounding tests, the tone-plus-odor compound occasioned more than double the responses occasioned by either the tone or odor presented individually. Thus, the current study (1) established stimulus control with an ambient olfactory discriminative stimulus in a traditional free-operant setting and (2) extended the generality of stimulus-compounding effects by demonstrating additive summation when olfactory and auditory discriminative stimuli were presented simultaneously.