DETECTION OF INCREMENTS IN NOISE INTENSITY BY MONKEYS¹

Abstract

Monkeys were trained to detect 100-msec increments in the intensity of continuous white noise. A response on one of two bars was reinforced with some probability if it conformed to the presence or absence of the increment on that trial. Stimulus parameters of background intensity, increment size, and probability of increment presentation were varied, and response probabilities and latencies were recorded. The task was analogous to the "yes-no" task used in human psychophysics. Data analysis within the context of signal-detection theory revealed response biasing toward one bar or the other to be related to the probability of increment presentation, whereas sensitivity depended on the combination of increment size and background noise intensity. Weber's law was found to hold for a large range of background intensities in that the sensitivity to relative intensity increments varied little. Performance was compared to that of an ideal observer that uses samples of the envelope of the noise waveform on which to base its responses.

Towards a behavioral theory of bias in signal detection

“…Thus: log (;:) -log (;:) = 2 log d. (8) both animal and human subjects has shown that, while a subject's ability to discriminate between two stimuli remains constant, he may be induced to change his response probabilities in the presence of each of the two stimuli. In these studies, response bias (or criterion) has commonly been manipulated by varying the probability of presenting one of the two stimuli (e.g., Clopton, 1972;Elsmore, 1972;Galanter & Holman, 1967;Hume, 1974aHume, , 1974bHume & Irwin, 1974;Markowitz & Swets, 1967;Schulman & Greenberg, 1970;Swets, Tanner, & Birdsall, 1961;Terman & Terman, 1972). We have shown, however, that response bias is not a function of stimuluspresentation probability but, rather, is a function of the relative reinforcement frequency obtained for the choice responses.…”

Auditory detection and optimal response biases

“…When stimulus parameters are held constant, the detectability of a signal is typically found to remain constant and independent of changes in response bias. These findings have been obtained both with humans (Tanner & Swets, 1954;Swets, Tanner, & Birdsall, 1961;Green & Swets, 1966;Galanter & Holman, 1967, Markowitz & Swets, 1967Schulman & Greenberg, 1970) and with animals (Stubbs, 1968;Clopton, 1972;Elsmore, 1972;Terman & Terman, 1972;Hume & Irwin").…”

Optimal response biases and the slope of ROC curves as a function of signal intensity, signal probability, and relative payoff

“…The animals' sensitivity to increments in the intensity of random noise increased with the magnitude of the signal, and was independent of variations in response bias induced by varying either the signal probability or the relative payofffor correct responses (cf, Stubbs, 1968;Irwin & Terman, 1970;Terman, 1970;Clopton, 1972;Terman & Terman, 1972;Hume & Irwin, 1974;Hume, 1974).…”

“…Both ROC curves and their complementary bias functions have been obtained in stud ies with' animals *This research constituted a portion of a thesis submitted in partial fulfillment of the requirements for the PhD degree at the University of Auckland. The research was supported in part by grants from the New Zealand University Grants Committee and the Scientific Distribution Committee to R. J. by varying either the signal probability (Clopton, 1972;Elsmore, 1972;Hodos & Bonbright, 1972;Terman & Terman, 1972;Hume & Irwin, 1974;Hume, 1974) or the symmetry of the reinforcement contingencies (Stubbs, 1968;Hume, 1974). To date, only Terman and Terman (1972) have considered how response biases may vary as a joint function of the signal probability and the stimulus parameters.…”

“…The result, when obtained, has been interpreted as representing an increase in the variance associated with the sianal as its intensity is increased, or it has been explained by assuming the distributions underlying the stimuli to be Rayleigh or exponential (Green & Swets, 1966, Chap. 3;Clopton, 1972). The only studies with animals reporting changes in the slope of the ROC curves with variations in signal intensity are those of Hack (1963Hack ( , 1966.…”