A simple stimulus generator for evoked response studies

An inexpensive computer-driven bipolar stimulator is described. The device produces variable-duration bipolar click stimuli for use in auditory evoked response studies, but is applicable to other research. The unit is driven directly from the digital input/output interface of the averaging computer, and temporal parameters are completely controlled by the machine.     

Novelty, stimulus control, and operant variability

Although behavior analysis has been criticized for failure to account for response novelty, many common behavior-analytic concepts and processes (e.g., selectionism, the operant, reinforcement, and stimulus control) assume variability both in the environment and in behavior. The importance of the relation between variability and novelty, particularly for verbal behavior, is discussed, and concepts used to account for novel behavior are examined. Experimental findings also are reviewed that suggest that variability in behavior can come under discriminative control, and these findings are applied to describe novel instances of behavior that may arise during problem solving. We conclude that variations provided and selected by the terms of the three-term contingency are powerful means for understanding novel behavior.     

Discriminated response and incentive processes in operant conditioning: a two-factor model of stimulus control

Understanding stimulus control generated in instrumental learning requires the direct investigation of discriminated response and reinforcer (incentive) processes acquired exclusively through the response-reinforcer contingencies operating on complex (multicomponent) baselines. Two series of stimulus-compounding studies accomplished this direct investigation. In one series, the independent variable was the relative reinforcement between schedule components; in the second series, it was relative response rate between components. Stimulus-compounding tests revealed that response and incentive processes enhanced each other when in agreement, counteracted each other when in opposition, and produced intermediate results when only one factor was operating. This pattern of results led to the conclusion that these factors were algebraically combining and to the development of a response/incentive matrix reflecting these dynamics. This two-factor analysis was extended to the peak-shift effect in stimulus generalization experiments and to the generation of inhibitory control. Two decades of stimulus compounding and peak-shift research were organized within this two-factor framework, extending this traditional approach to learning to active research areas heretofore not systematically considered in these terms.     

Design and evaluation of a touchscreen apparatus for operant research with pigeons

We developed a touchscreen apparatus for pigeons and conducted a series of experiments that assessed its utility for free-operant procedures. The apparatus incorporated an on-board Windows computer, an electromechanical interface, an amplified speaker, and the touchscreen. We found that merely projecting a virtual key on the screen was insufficient; too many pecks missed the key. Adding a visual target in the center of the key and providing visual feedback for on-key pecks both failed to improve response accuracy. Accuracy was improved by imposing a timeout after off-key pecks or providing a physical boundary around the key. With the physical boundary, response accuracy was comparable to that obtained with conventional plastic keys, and response acquisition via autoshaping also was comparable. Mixing the color elements of the screen's pixels produced color stimuli, but the colors did not function as pure wavelengths of light in tests of stimulus generalization. Both colors and geometric shapes functioned as discriminative stimuli in multiple schedules with variable-interval and extinction components or rich and lean fixed-ratio components. In general, our touchscreen apparatus is a viable alternative to conventional pigeon chambers and increases the experimenter's options for visual stimuli, auditory stimuli, and the number and location of response keys.     

Multiple‐stimulus preference assessments: a comparison of free‐operant and restricted‐operant formats

We compared free‐operant and restricted‐operant multiple‐stimulus preference assessments with three children diagnosed with mental retardation. The methods produced comparable results, although the free‐operant assessment identified fewer potential reinforcers than the restricted‐operant assessment. The highest‐ and lowest‐ranked stimuli from both methods were subsequently evaluated in a concurrent‐operants reinforcer assessment. All participants engaged in behavior that resulted in access to the highest‐ranked stimuli the majority of the time, thus validating both preference assessment methods as effective in identifying reinforcers. Copyright © 2000 John Wiley & Sons, Ltd.     

New methodology in infant operant kicking procedures: computerized stimulus control and computerized measurement of kicking

Numerous developmental issues have been assessed using a mobile reinforcement procedure (leg kicks=operant response, movement of a 3D mobile=reinforcer). The current study addressed issues of stimulus control in the mobile procedure through implementation of computerized measurement of leg kicks and computerized control over auditory/visual reinforcers. Experiment 1 demonstrated that the computerized apparatus provides a sensitive measure of learning and memory. Experiment 2 examined the efficacy of single and multiple modality reinforcement in learning/retention of operant kicking and revealed successful acquisition with single modality reinforcement. These results suggest that the mobile procedure could be expanded to address other types of developmental questions (i.e. perception, cognition, intersensory integration) and could be modified to allow replacement of the 3D mobile with images displayed on a computer monitor, thereby extending the utility of the procedure to studies requiring precise psychophysical control over visual stimuli (i.e. object identification and categorization).     

Sharing in preschool children: Facilitation, stimulus generalization, response generalization, and maintenance

Three approaches to facilitating verbal and physical sharing and of the generalizability and durability of the behaviors that were trained were investigated. During a free play period, groups of preschool children were taught to share verbally, to share physically, or to share verbally and physically; another group was not trained. Immediately following free play, the children were observed in a different setting. Follow-up was conducted 4 weeks after training ended. Physical sharing that was durable and generalizable resulted only when children were taught to share verbally. Increases in physical sharing produced by training children to share only physically were not durable and did not generalize. Training both verbal and physical sharing produced results with a magnitude slightly greater than teaching just verbal sharing. Despite a lack of special programming, some of the treatment effects generalized to another setting and were maintained during the Follow-up. There was response generalization of the effects of training verbal sharing to physical sharing but not vice versa. Problems with the concept of response class, a methodological suggestion for studying response generalization, and possibilities concerning why generalization and maintenance occurred without specific programming are discussed.     

Exemplar and prototype models revisited: response strategies,selective attention,and stimulus generalization

J. D. Smith and colleagues (J. P. Minda & J. D. Smith, 2001; J. D. Smith & J. P. Minda, 1998,2000; J. D. Smith, M. J. Murray, & J. P. Minda, 1997) presented evidence that they claimed challenged the predictions of exemplar models and that supported prototype models. In the authors' view, this evidence confounded the issue of the nature of the category representation with the type of response rule (probabilistic vs. deterministic) that was used. Also, their designs did not test whether the prototype models correctly predicted generalization performance. The present work demonstrates that an exemplar model that includes a response-scaling mechanism provides a natural account of all of Smith et al.'s experimental results. Furthermore, the exemplar model predicts classification performance better than the prototype models when novel transfer stimuli are included in the experimental designs.     

Choice, time allocation, and response rate during stimulus generalization

Six pigeons were trained to discriminate between two noise intensities using a procedure that assessed choice, time allocation, and response rate simultaneously and independently. Responses on the left or right key (R1 or R2) were respectively correct in the presence of two different intensities, S1 and S2. After a correct response, reinforcement became available for pecks on the center key. Reinforcement density for R1¦S1 relative to R2¦S2 was varied across experimental conditions. Generalization tests followed extensive training at each condition. As a function of stimulus intensity, proportions of initial choices of R2, of time spent in R2-initiated components, and of center-key responses emitted in R2-initiated components all yielded sigmoidal gradients of similar slope, which shifted slightly in location when relative reinforcement density changed. Changeovers were maximal where initial choice proportions approximated 0.5. Gradients relating the absolute number of center-key responses to stimulus intensity were also roughly sigmoidal, but were more sensitive to changes in reinforcement density. Gradients of momentary response rate also depended on reinforcement density. During training, large but transitory shifts in choice responding occurred when reinforcement density changed, while differences in momentary response rate developed slowly, suggesting separate control of choice and response rate by the contingencies of reinforcement.     

Duration comparison: relative stimulus differences stimulus age, and stimulus predictiveness.

Under a psychophysical trials procedure, pigeons were presented with a red light of one duration followed by a green light of a second duration. Eight geometrically spaced base durations were paired with one of four shorter and four longer durations as the alternate member of a duration pair, with different pairs randomly intermixed. One choice was reinforced if red had lasted longer than green, and a second choice was reinforced if green had lasted longer. Performance was compared when all the base durations and their pair members were included (entire-range condition) or when only the four longest base durations and their comparison durations (restricted-range condition) were used. Discrimination sensitivity decreased for longer duration pairs under both conditions, supporting a memory-based account. Sensitivity was lower under the restricted-range condition. Under both conditions, a bias to report "green as longer" increased as the second green duration increased. Bias changed as a matching function of the green-duration predictiveness of the correct choice. The results are related to a quantitative model of timing and remembering proposed by Staddon.     

Using the Macintosh computer in psychophysiological research: Programs for stimulus presentation,data collection,and response quantification

In this paper, we describe two Turbo Pascal programs, one for the control of stimulus presentation and measurement with peripheral devices (BLINK) and another for off-line stimulus reduction and analysis (SCORE). The programs can be applied in a wide variety of research settings. The programs do not use all of the interactive features of the pull-down menus found in the Macintosh, which increases the degree to which they can be modified for local use. They do not require familiarity with programming.     

Effects of varying length of stimulus series and response scale upon response latency,response uncertainty,and transmitted information

A 3 by 3 orthogonal design was employed t o study the interrelations among response latency (RL), response uncertainty (E_R), and transmitted information Nine groups of Ss judged the size of 5, 20, or 40 projected squares in terms of 5, 20, or 40 response categories. Patterns of change in ER and RL over the three stimulus series were differentially effected by increases in the number of available response categories. The increase from 5 to 20 response categories produced, for successively longer stimulus series, a constantly increasing change in E_R; the further increase from 20 to 40 categories produced a contrasting, constantly decreasing change in E_R. The same two changes in number of response categories produced the same pattern of change in RL over the 5- and 20-stimulus series but reversed the pattern for the 40-stimulus series. Correlations between E_R and RL ranged from .28 to .99 and tended to maximize when number of response categories equaled the number of stimuli. I_t was relatively low under all conditions. Within the 5- and 20-stimulus series, increases from 5 to 20 to 40 available responses increased RL in a negatively accelerated fashion but did not increase I_t. Within the 40-stimulus series, the same increases in number of available responses produced an essentially linear increase in both I_t and RL.