DISPLACEMENT OF LEISURE REINFORCERS BY FOOD DURING PREFERENCE ASSESSMENTS

Identification of reinforcers for individuals with developmental disabilities is often based on the outcome of preference assessments in which participants make selections from among a variety of items. We determined the extent to which individuals might show a general preference for food items over leisure items during such assessments and whether leisure items that are “displaced” by food items might nevertheless function as reinforcers. Arrays consisting of food items only and then nonfood items only were presented separately to 14 participants and then were ranked to determine preference. The top selections from these initial assessments were subsequently combined in a third assessment, and preferences were again established. All but 2 participants showed a general preference for food items, such that selection of nonfood items in the combined arrays was displaced downward relative to selection of nonfoods in the nonfood-only arrays. Two of the participants were exposed to a condition in which a nonfood item was delivered contingent on the occurrence of an adaptive response, and increased rates of responding by both individuals were observed. Results are discussed in terms of limitations posed by using only food items as reinforcers and the resulting need to take precautionary measures when attempting to identify nonfood reinforcers.     

Dissociating prelexical and postlexical processing of affective information in the two hemispheres: effects of the stimulus presentation format

Using a lexical decision task, the authors investigated whether brain asymmetries in the detection of emotionally negative semantic associations arise only at a perceptually discriminative stage at which lexical analysis is accurate or can already be found at crude and incomplete levels of perceptual representation at which word-nonword discrimination is based solely on guessing. Emotionally negative and neutral items were presented near perceptual threshold in the left and right visual hemifields. Word-nonword discrimination performance as well as the bias to classify a stimulus as a "word" (whether or not it actually is a word) were assessed for a normal, horizontal stimulus presentation format (Experiment 1) and for an unusual, vertical presentation format (Experiment 2). Results show that while the two hemispheres are equally able to detect affective semantic associations at a prelexical processing stage (both experiments), the right hemisphere is superior at a postlexical, perceptually discriminative stage (Experiment 2). Moreover, the findings suggest that only an unusual, nonoverlearned stimulus presentation format allows adequate assessment of the right hemisphere's lexical-semantic skills.     

Conditional discrimination with ambiguous stimuli.

Five pigeons learned a two-key conditional discrimination. When background color on both keys was red, pecks on the key with a horizontal line produced food. When the color was green, pecks on the key with a vertical line produced food. During part of the experiment, color was presented on only one of the keys. It was found that accuracy was higher when color was combined with the line stimulus correlated with nonreinforcement. In another part of the experiment, color was presented on both keys but a line was present only on one. Accuracy was higher when the line accompanied the nonreinforced option than when the line accompanied the reinforced option. Superior performance when the combined stimuli were displayed on the nonfood key may be explained by the association of different components of the compound stimuli with reinforcement or as the result of rules pigeons follow in solving conditional discriminations.     

ASSESSING CHOICE MAKING AMONG CHILDREN WITH MULTIPLE DISABILITIES

Some learners with multiple disabilities display idiosyncratic gestures that are interpreted as a means of making choices. In the present study, we assessed the validity of idiosyncratic choice-making behaviors of 3 children with multiple disabilities. Opportunities for each child to choose between food and drink were provided under two conditions. In one condition, the children were given the food or drink item corresponding to their prior choice. In the other condition, the teacher delivered the item opposite to that chosen. It was reasoned that valid choice-making behaviors would be reflected in a greater tendency to accept the chosen item and refuse the unchosen item. Direct observations revealed all children consistently indicated choices during both conditions. Choices of both the food and drink items were made by all 3 children. A reversal design demonstrated that acts of refusal were more frequent when choices were followed by delivery of the item opposite to that chosen. Similar assessment procedures may be effective in determining the function of idiosyncratic gestures exhibited by persons with multiple disabilities. For children lacking such skills, intervention to teach valid choice-making behaviors may be needed to complement assessment procedures.     

The Effects of Subject-Defined Categories on Judgmental Accuracy in Confidence Assessment Tasks

The accuracy of confidence judgments can be determined using measures of discrimination and calibration. The present paper utilizes a new assessment methodology that decomposes the confidence assessment task, allowing us to investigate discrimination and calibration skills in greater depth than has been done in previous studies. Researchers investigating the goodness of confidence judgments have typically grouped forecasters' assessments into experimenter-defined categories, generally in equal widths of .10. In the present research, subjects created their own categories and later assigned confidence judgments to the categories, separating the tasks of discriminating categories (discrimination) and assigning numbers to categories (calibration). Further, the typical assessment procedure assumes that subjects are able to discriminate equally across the confidence scale. Since subjects in the present study defined their own assessment categories, they could locate those categories at any point on the scale. A final issue of interest was whether subjects were able to determine accurately the number of categories into which they could discriminate. Sixty subjects performed 1 of 2 tasks, general knowledge or forecasting, in both relatively easy and relatively hard conditions. Results showed a trade-off in performance: Calibration generally became worse as the number of categories increased, while discrimination generally improved. Overall accuracy was not affected by the number of categories used. Further, subjects partitioned categories more at the high end of the scale. Finally, measures showed that subjects were not accurate in their beliefs about their own discrimination ability.     

Short-Term Retention of “Surprising” Events By Pigeons

Terry and Wagner (1975) have suggested that the short-term retention of information about an event is enhanced if the occurrence of the event is made unexpected or surprising. Three experiments tested this idea using delayed conditional position (Experiment I) and colour discriminations (Experiments II and III). The subjects were pigeons and the presentation of food was the target event to be remembered. Choice of one of two simultaneously presented stimuli was reinforced if the retention interval had been initiated by presentation of target food. Contrary to Terry and Wagner's claim, retention was superior on probe test trials in Experiments I and II if the presentation of the target food was preceded by a previously established signal for food (CS+) rather than by a stimulus which had not been paired with food (CS-). Experiment III systematically manipulated the signalling conditions used during initial discrimination training. Retention was better following a CS+ presentation if the target food had been signalled during initial discrimination training but worse if the food presentation had been unsignalled. These results do not favour the idea that retention of an event is directly affected by whether or not the target event is surprising.     

Conditional Reinforcers and Informative Stimuli in A Constant Environment

Five pigeons responded on steady-state concurrent variable-interval variable-interval schedules of food presentation in which half of the foods were removed and replaced with nonfood stimuli. Across conditions, the stimuli were either paired or unpaired with food, and the correlation between the ratio of food deliveries on the two alternatives and the ratio of nonfood stimuli was either −1, 0, or +1. Neither the pairing of stimuli with food, nor the correlation between stimuli and food, affected generalized-matching performance, but paired stimuli had a demonstrable effect at a local level of analysis. This effect was independent of the food–stimulus correlation. These results differ from results previously obtained in a frequently changing environment. We attribute this difference in results to differences in the information value of response-contingent stimuli in frequently changing versus relatively constant environments, as well as to differences between forward pairing and simultaneous pairing of the stimuli with food.     

Another dimension for assessment of speech-sound discrimination: latency of response.

The relationship of speech-sound-discrimination skills and speed of responding was investigated by presenting monosyllabic nouns in three different listening conditions to a total of 72 nursery, kindergarten, and first-grad children divided into three equal-sized groups. Speed of responding was related to the age of subjects, accuracy of responding, and context of presentation of stimulus items. There was a consistent decrease in latency of responding as age increased. Error responses had greater response latencies than correct responses. Response latencies for different contexts of presentation of stimulus items were longest for the paired-comparison context and shortest for the carrier-phrase context. Speed of responding could be considered as an additional parameter when evaluating speech-sound-discrimination skills.     

Conditional discrimination in mentally retarded adults: the development of generalized skills.

The development of generalized conditional discrimination skills was examined in adults with retardation. Two subjects with histories of failure to acquire arbitrary matching under trial-and-error procedures were successful under procedures that trained one or more prerequisite skills. The successive discrimination between the sample stimuli was established by training the subjects to name the stimuli. The simultaneous discrimination between the comparison stimuli was established using either (a) standard simple discrimination training with reversals or (b) a procedure in which each of the two sample-comparison relations in the conditional discrimination was presented in blocks of trials, with the size of the blocks decreasing gradually until sample presentation was randomized. The amount of prerequisite training required varied across subjects and across successive conditional discriminations. After acquiring either two or three conditional discriminations with component training, both subjects learned new conditional discriminations under trial-and-error procedures. In general, each successive conditional discrimination was acquired more rapidly. Tests showed that conditional responding had become a generalized skill. Symmetry was shown for almost all trained relations. Symmetry trial samples were ultimately named the same as the stimuli to which they were related in training.     

Memory for modality of presentation: Within-modality discrimination

Two experiments demonstrated that Ss are capable of making within-modality memory discriminations in both visual and auditory modalities. In Experiment I Ss studied mixed lists of pictures and labels representing common objects and were subsequently required to judge whether the original presentation was pictorial or verbal The high level of performance achieved on this task was unaffected by degree of categorical relatedness of items within method of presentation or by instructions to produce visual images when items were presented verbally. In Experiment II Ss demonstrated the ability to remember whether a sentence was originally presented by a male or a female speaker. Some strategies by which within-modality discrimination in memory might be accomplished are discussed.     

The discrimination of discrete and continuous amounts in African grey parrots (Psittacus erithacus)

A wealth of research in infants and animals demonstrates discrimination of quantities, in some cases nonverbal numerical perception, and even elementary calculation capacities. We investigated the ability of three African grey parrots (Psittacus erithacus) to select the largest amount of food between two sets, either discrete food items (experiment 1) or as volume of a food substance (experiment 2). The two amounts were presented simultaneously and were visible at the time of choice. Parrots were tested several times for all possible combinations between 1 and 5 seeds or 0.2 and 1 ml of food substance. In both conditions, subjects performed above chance for almost all combinations. Accuracy was negatively correlated with the ratio, that is performance improved with greater differences between amounts. Therefore, these results with both individual items and volume discrimination suggest that parrots use an analogue of magnitude, rather than object-file mechanisms to quantify items and substances.     

Numerical judgments by chimpanzees (Pan troglodytes) in a token economy

We presented four chimpanzees with a series of tasks that involved comparing two token sets or comparing a token set to a quantity of food. Selected tokens could be exchanged for food items on a one-to-one basis. Chimpanzees successfully selected the larger numerical set for comparisons of 1 to 5 items when both sets were visible and when sets were presented through one-by-one addition of tokens into two opaque containers. Two of four chimpanzees used the number of tokens and food items to guide responding in all conditions, rather than relying on token color, size, total amount, or duration of set presentation. These results demonstrate that judgments of simultaneous and sequential sets of stimuli are made by some chimpanzees on the basis of the numerousness of sets rather than other non-numerical dimensions. The tokens were treated as equivalent to food items on the basis of their numerousness, and the chimpanzees maximized reward by choosing the larger number of items in all situations.     

A mechanistic account of the mirror effect for word frequency: a computational model of remember-know judgments in a continuous recognition paradigm

A theoretical account of the mirror effect for word frequency and of dissociations in the pattern of responding Remember vs. Know (R vs. K) for low- and high-frequency words was tested both empirically and computationally by comparing predicted with observed data theory in 3 experiments. The SAC (Source of Activation Confusion) theory of memory makes the novel prediction of more K responses for high- than for low-frequency words, for both old and new items. Two experiments used a continuous presentation and judgment paradigm that presented words up to 10 times. The computer simulation closely modeled the pattern of results, fitting new Know and Remember patterns of responding at each level of experimental presentation and for both levels of word frequency for each participant. Experiment 3 required list discrimination after each R response (Group 1) or after an R or K response (Group 2). List accuracy was better following R responses. All experiments were modeled using the same parameter values.     

Effects of associatively significant posttrial stimuli on learning and memory

Pigeons were trained on a delayed conditional discrimination in which the choice between two simultaneously presented stimuli depended on how the trial started. Choice of one of the stimuli was reinforced if the trial had been initiated by presentation of a food sample and choice of the other was reinforced if no sample had been presented. Subsequently, test trials were administered on which an associatively significant stimulus was presented during the retention interval. This manipulation was intended to modulate the short-term retention of information about the food sample. It was found that performance on food sample test trials was enhanced by presentation of an excitor for food, disrupted by presentation of an inhibitor for food and unaffected by presentation of an associatively neutral stimulus. The impact of these posttrial stimuli was also assessed on the ability of the food sample to serve as a reinforcer. This was done by recording the development of responding to a keylight that signalled the food sample on these test trials. Compared to the associatively neutral stimulus, both the excitor and the inhibitor interfered with the development of keypecking. These results are discussed with regard to the issue of how posttrial events modulate associative learning.     

Effects of percentage occurrence of response members and its method of presentation on verbal discrimination learning and transfer

Each of 144 Ss learned two verbal discrimination (VD) lists for six trials. Two levels of percentage occurrence of response members (100% or 50%) were combined factorially with two methods of presentation and three transfer paradigms (C₁-I₂, C₂-I₁, C₂-I₂). In first-list learning, with one method of presentation in the 50,% ORM entire list was presented with only half the correct (C) items designated on each study trial, while in the second method only half the list was presented with all C items underlined. There were no differences between the two methods in the 100% ORM condition. The results indicated that % ORM was a significant variable in first-list learning, supporting the findings of Newby and Young (1972). No effect was found for method of presentation. Also, no real significant effect of these two variables was found in VD transfer. All results were interpreted in terms of the frequency theory of VD learning.     

Functional assessment and treatment of pica: a single‐case experiment

The pica of a 6‐year‐old girl diagnosed with autism was initially shown to persist in the absence of socially mediated consequences. In an attempt to provide a competing source of oral stimulation, we used a stimulus preference assessment to identify food items that were subsequently presented noncontingently. However, the noncontingent schedule could not be thinned to a practical variation while still maintaining reductions in pica. A subsequent multielement evaluation of response blocking and verbal reprimands demonstrated that neither intervention both produced and maintained low levels of pica. Verbal reprimands were then used in conjunction with noncontingent food presentation, but this intervention did not produce significant reductions in pica. Suppression of pica was ultimately obtained in both a clinic setting and in the child's natural environment using contingent, varied auditory stimulation. The results are discussed in the context of the ‘least restrictive alternative’ model of treatment selection. Copyright © 2001 John Wiley & Sons, Ltd.     

Erratum to: Chimpanzees (Pan troglodytes) accurately compare poured liquid quantities

Although many studies have shown that nonhuman animals can choose the larger of two discrete quantities of items, less emphasis has been given to discrimination of continuous quantity. These studies are necessary to discern the similarities and differences in discrimination performance as a function of the type of quantities that are compared. Chimpanzees made judgments between continuous quantities (liquids) in a series of three experiments. In the first experiment, chimpanzees first chose between two clear containers holding differing amounts of juice. Next, they watched as two liquid quantities were dispensed from opaque syringes held above opaque containers. In the second experiment, one liquid amount was presented by pouring it into an opaque container from an opaque syringe, whereas the other quantity was visible the entire time in a clear container. In the third experiment, the heights at which the opaque syringes were held above opaque containers differed for each set, so that sometimes sets with smaller amounts of juice were dropped from a greater height, providing a possible visual illusion as to the total amount. Chimpanzees succeeded in all tasks and showed many similarities in their continuous quantity estimation to how they performed previously in similar tasks with discrete quantities (for example, performance was constrained by the ratio between sets). Chimpanzees could compare visible sets to nonvisible sets, and they were not distracted by perceptual illusions created through various presentation styles that were not relevant to the actual amount of juice dispensed. This performance demonstrated a similarity in the quantitative discrimination skills of chimpanzees for continuous quantities that matches that previously shown for discrete quantities.     

Quantity judgments of auditory and visual stimuli by chimpanzees (Pan troglodytes)

Many species can choose between two visual sets of stimuli on the basis of quantity. This is true when sets are both visible, or are presented one set at a time or even one item at a time. However, we know comparatively little about how well nonhuman animals can compare auditory quantities. Here, three chimpanzees (Pan troglodytes) chose between two sets of food items when they only heard each item fall into different containers rather than seeing those items. This method prevented the chimpanzees from summing the amount of visible food they saw because there were no visual cues. Chimpanzees performed well, and their performance matched that of previous experiments with regard to obeying Weber's law. They also performed well with comparisons between a sequentially presented auditory set and a fully visible set, demonstrating that duration of presentation was not being used as a cue. In addition, they accommodated empty sets into these judgments, although not perfectly. Thus, chimpanzees can judge auditory quantities in flexible ways that show many similarities to how they compare visual quantities.     

Examination of relative reinforcement effects of stimuli identified through pretreatment and daily brief preference assessments.

Several brief preference assessments have recently been developed to identify reinforcers for individuals with developmental disabilities. One purported advantage of brief assessments is that they can be administered frequently, thus accommodating shifts in preference and presumably enhancing reinforcement effects. In this study, we initially conducted lengthy paired‐choice preference assessments and identified a hierarchy of preferred items for 5 individuals with developmental disabilities. Subsequently, brief multiple‐stimulus‐without‐replacement assessments using the same items were completed each day prior to work sessions. On days when results of the daily brief assessment differed from the one‐time lengthy assessment, the relative reinforcing effects of the top items from each assessment were compared in a concurrent‐schedule arrangement. The results revealed that when the two assessments differed, participants generally allocated more responses to the task associated with the daily top‐ranked item.     

A configural analysis for feature-negative discrimination learning.

In 4 experiments, rats were initially trained with an A+ AXo discrimination in which Stimulus A by itself signaled the delivery of food, A+, whereas the simultaneous presentation of A and X was followed by nothing, AXo. In each experiment X was then paired with food prior to a test phase in which A and X were again presented for a discrimination. The discrimination was of the form A+ AXo in Experiments 1 and 2, whereas it was of the form X+ AXo for Experiments 3 and 4. In all 4 experiments the test discrimination was acquired more rapidly than a control discrimination. The results are interpreted in terms of the original A+ AXo discrimination resulting in the growth of an association between a representation of the entire AX compound and the effects of nonreinforcement.