The effect of irrelevant surround on speeded visual discriminations varying in complexity

To measure the effect of varying stimulus material on visual matching, a three-factor experimental design was employed, with “same”-“different” RT as the main dependent variable. Pairs of sequences of meaningless shapes served as stimuli, varying in discriminability (high or low), complexity (sequence lengths of 1, 2, 5, or 8 shapes), and level of pair difference (identical sequences or sequences with one pair differing). All independent variables significantly affected RT, with (a) high-discriminability stimuli being reacted to faster than low, (b)RT increasing with sequence pair length, and (c)“same”-response RTs interacting with “different”-response RTs. A significant triple-order interaction component implied that, while a single-process self-terminating feature testing model could accommodate data from the low-discriminability condition, the high-discriminability data did not fit this model. The results are taken as support for a dual-process model to account for the data from “same”-“different” RT tasks. epaxtment of     

Pavlovian processes and response competition as determinants of avoidance response-prevention effects

Two experiments investigated the facilitation of avoidance extinction by exposure to lengthy (5-sec) shock during avoidance response prevention. In Experiment 1, animals exposed to light only or to light-shock pairings during response prevention showed equal facilitation of extinction relative to shock-only animals or to animals receiving no response prevention. Preshock rearing, directly antagonistic to the avoidance response, developed for shocked animals during response prevention and persisted during extinction for light-shock animals. Immediately before extinction, half of each group was permitted a single escape from a light-shock compound by means of the response previously required for avoidance. The only effect was upon the extinction performance of light-shock animals. Rearing was eliminated and extinction responding increased to a level far above that for any of the other animals. Experiment 2 demonstrated that the shock-only treatment affected the extinction performance and rearing of nonescape and escape animals in a manner entirely equivalent to the effects of the light-shock treatment of Experiment 1, provided stimulus conditions (light absent) were the same for all experimental phases. Thus, lengthy shock during avoidance response prevention simultaneously leads to the acquisition of competing behavior and enhances control by a warning signal or contextual stimuli over the avoidance response. Implications for the CS-only response-prevention treatment and the transfer of aversive control are discussed.     

Factor-derived categories of chronic aphasia

A large sample of patients with aphasia (N = 118), unselected for etiology, were administered the Porch Index of Communicative Ability more than 6 months after the onset of aphasia. Factor analysis of PICA subtest scores identified five factors which accounted for 83.9% of the total variance. The factors were labeled speaking, writing, comprehension, gesturing, and copying. Cluster analyses of the factor scores yielded five patient categories which differed in the pattern of impairment on the language factors as well as in overall severity of aphasia. A subgroup of the parent sample consisting of 52 patients with localized left-hemisphere CVA had cluster analyses repeated after having first been studied as part of the larger sample. The factor-derived categories for the subgroup were similar to those of the entire group. Discriminant functions of the PICA raw scores of the 52-patient subsample correctly classified all of the patients. When discriminant functions were based upon the factor scores of the 118-patient parent sample, 80.7% of the 52 patients were correctly classified into the five categories.     

TRAINING AND GENERALIZATION OF LAUNDRY SKILLS: A MULTIPLE PROBE EVALUATION WITH HANDICAPPED PERSONS

An instructional procedure composed of a graded sequence of prompts and token reinforcement was used to train a complex chain of behaviors which included sorting, washing, and drying clothes. A multiple probe design with sequential instruction across seven major components of the laundering routine was used to demonstrate experimental control. Students were taught to launder clothing using machines located in their school and generalization was assessed later on machines located in the public laundromat. A comparison of students' laundry skills with those of normal peers indicated similar levels of proficiency. Follow-up probes demonstrated maintenance of laundry skills over a 10-month period.     

A further parallel between selective adaptation and contrast

It is generally believed that selective adaptation effects in speech perception are due to a reduction in sensitivity of auditory feature detectors. Recent evidence suggest that these effects may derive instead from contrast. In a further test of the contrast hypothesis, we conducted two experiments each involving both adaptation and contrast sessions with matching stimulus sets. During the adaptation sessions of Experiment 1, subjects identified two series of velar stimuli varying in voice onset time, [ga]-[kha] and [gi]-[khi], before and after adaptation with of the following stimuli: [ga], [kha], [gi], and [khi]. In the contrast session, subjects identified either of two ambiguous test items (drawn from near the phonetic boundaries of the [ga]-[kha] and the [gi]-[khi] series) following a single presentation of [ga], [kha], [gi], or [khi]. For both the adaptation and contrast sessions, (a) the [--a] test items were more greatly affected (in a contrast direction) by the [--a] than by the [--i] adaptor/context stimuli, and (b) the [--i] test items were not differentially affected by the [--1] and [--i] adaptor/context stimuli. An analogous design was used in Experiment 2, except that the stimulus sets varied in pitch rather than vowel quality. For both the adaptation and contrast sessions, the test items were not differentially affected by the pitch of the adaptor/context stimulus. These parallel results provide further evidence that adaptation effects are actually a form of contrast.     

A flexible computer-controlled perception laboratory

Research in perception is often guided or limited by the capabilities of the laboratory. A computer-controlled perception laboratory is described that was designed to be extremely flexible at a modest cost. The laboratory permits control of onset time, offset time, and intensity of visual, auditory, and tactile stimuli. The visual stimuli include single points, text, stereoscopic displays, and two-dimensional representations of three-dimensional objects moving in space. The design of the hardware and software and the criteria that guided our choice of this design are discussed. Finally, potential applications of this laboratory are considered.     

Psychological re-evaluations: A survey of practices and perceptions of school psychologists

The practice of psychologically re-evaluating students receiving special education services has been mandated by P.L. 94–142 and further operationalized by state departments of education. Intuitively, such a requirement appears sound, for psychologists occasionally make mistakes, children change over time, and efficacy of special education services is variable. Yet given the other mandated practices, such as yearly IEP updates, and the fact that many school psychologists spend a majority of their time testing, we wondered how important three-year psychological re-evaluations are considered by school psychologists. In the present study 40 psychologists across four states were surveyed concerning their perceptions and practices regarding re-evaluations. The psychologists' responses to a 16-item questionnaire indicated that re-evaluations comprised a substantial portion of their evaluations, involved a considerable amount of time, and were perceived as an important check on a child's diagnosis and placement. Re-evaluations and initial evaluations were described as involving nearly identical tests and related activities.     

ANALYSIS OF FREE-TIME CONTINGENCIES AS POSITIVE VERSUS NEGATIVE REINFORCEMENT

Providing a short break contingent on completed work may increase responding through positive reinforcement (e.g., access to preferred activities) or negative reinforcement (e.g., escape from work). In this investigation, three analyses conducted with a boy with profound mental retardation showed that (a) a 20-s break increased responding more than a positive reinforcer (cola) did, and (b) the reinforcing effects of a 20-s break were affected by the availability of positive reinforcers during the break.     

FURTHER ANALYSIS OF THE RELATIONSHIP BETWEEN SELF-INJURY AND SELF-RESTRAINT

It has been suggested that self-restraint, a phenomenon often correlated with self-injurious behavior (SIB), may be maintained by negative reinforcement in the form of escape from the aversive properties of SIB (e.g., pain). We examined the effects of blocking SIB (and presumably removing any aversive effects) on the self-restraint of a 19-year-old male with severe mental retardation. Consistent with the negative reinforcement hypothesis, blocking SIB resulted in near-zero levels of SIB and moderate reductions in self-restraint.