Psychometric Functions For Discrimination Research Articles

Empirical Performance of Optimal Bayesian Adaptive Estimation

Simulation studies have shown how Bayesian adaptive estimation methods should be set up for optimal performance. We assessed the extent to which these results hold up for human observers, who are more subject to failure than simulation subjects. Discrimination and detection experiments with two-alternative forced-choice (2AFC) tasks were used for that purpose. Forty estimates of the point of subjective equality (PSE, or the 50% correct point on the psychometric function for discrimination) and 32 estimates of detection threshold (the 80% correct point on the psychometric function for detection) were taken for each of four observers with the optimal Bayesian method, while data for fitting the psychometric function psi were gathered concurrently with an adaptive method of constant stimuli governed by fixed-step-size staircases. The estimated parameters of the psychometric function served as a criterion for comparison. In the discrimination task, PSEs for each observer were distributed around the independently estimated 50% correct point on psi and their variability was occasionally minimally larger than simulation results indicated it should be. In the detection task, the distribution of threshold estimates was consistently above the independently estimated 80% correct point on psi and their variability was as expected from simulations. A close analysis of these results suggests that the optimal Bayesian method is affected by growing inattention or fatigue in detection tasks (factors that are not considered in simulations), and limits the practical applicability of Bayesian estimation of detection thresholds.

Using distinctive Fourier components to discriminate between complex patterns.

Observers discriminated between a plaid pattern formed by summing vertical and horizontal cosine gratings, and a plaid formed by multiplying the gratings. Such patterns are alike with respect to many non-Fourier primitives, but differ in the Fourier domain by diagonal components which are present in the plaid formed by multiplication, but not in the one formed by summing. When discrimination performance is related to the contrast of the diagonal components, it is found that the contrast threshold for discrimination is approximately the same as the threshold for detection of the isolated components. However, the psychometric function for discrimination is shallower than that for detection, suggesting the presence of masking. Despite the masking, the results support the proposition that discrimination processes may operate directly on the representations of local Fourier components.

Comparison of Detection and Discrimination of Tones of Different Durations under Homophasic and Antiphasic Conditions

Using a two-alternative temporal forced-choice technique (2ATFC), the detectability of both a 64-and a 128-msec 500-Hz signal in a continuous noise masker (50 dB spectrum level) was determined. The ability of the observers to discriminate the long from the short tone was also measured using a similar psychophysical technique. Both detectability and duration discriminability were measured with both homophasic (N0-S0) and antiphasic (N0-Sπ) conditions. Under the homophasic condition, the observers require only slightly greater signal energy (approximately 3 dB) in order to perform as well in the discrimination task as they do in the detection task. With the antiphasic condition, the psychometric function for discrimination is not only displaced considerably toward greater signal energies, relative to those required for detection, but the slope of the function for discrimination is less than that for detection.