Performance of humans in variable-interval avoidance schedules programmed singly, and concurrently with variable-interval schedules of positive reinforcement

Performance maintained under single variable-interval avoidance schedules, single variable-interval schedules of positive reinforcement, and concurrent schedules consisting of a variable-interval avoidance component and a variable-interval positive reinforcement component, was studied in three human subjects, using points exchangeable for money as the reinforcer. Response rate in the single variable-interval avoidance schedules was an increasing function of the frequency of monetary loss avoidance. Response rate in the single variable-interval positive reinforcement schedules was an increasing function of the frequency of obtained monetary reinforcement. In the concurrent avoidance/reinforcement schedules, the rate of responding in the avoidance component increased, and the rate of responding in the positive reinforcement schedule decreased (with one exception) as a function of the frequency of loss avoidance in the avoidance component. The logarithms of the ratios of the response rates in the two components, and the logarithms of the ratios of the times spent in the two components, were linearly related to the logarithms of the ratios of the frequency of loss avoidance in the avoidance component to the frequency of reinforcement in the positive reinforcement component. All three subjects exhibited marked undermatching of response rate ratios to reinforcement frequency ratios. The results are discussed in the context of Herrnstein's quantitative model of operant performance.     

Temporal integration and contrast sensitivity in foveal and peripheral vision

Spatial contrast sensitivity functions and temporal integration functions for gratings with dark surrounds were measured at various eccentricities in photopic vision. Contrast sensitivity decreased with increasing eccentricity at all exposure durations and spatial frequencies tested. The decrease was faster at high than at low spatial frequencies, but similar at different exposure durations. When cortically similar stimulus conditions were produced at different eccentricities by M-scaling, contrast sensitivity became independent of visual field location at all exposure durations tested. The results support the view that in photopic vision spatiotemporal information processing is qualitatively similar across the visual field, and that quantitative differences result from retino-topical differences in ganglion cell sampling. For gratings of constant retinal area temporal integration (improvement of contrast sensitivity with increasing exposure duration) was more extensive at high than at low retinal spatial frequencies but independent of cortical spatial frequency and eccentricity. For M-scaled gratings temporal integration was more extensive at high than at low cortical spatial frequencies but independent of retinal spatial frequency and eccentricity. The results suggest that the primary determinant of temporal integration is not spatial frequency but grating value that is calculated as AF2 square cycles (cycle2), where A is grating area and F spatial frequency.