Mechanisms of simultaneous color induction.

A new method of measuring simultaneous contrast, or chromatic induction, is introduced and used to test the hypotheses that induction results from either multiplicative or subtractive interaction of either like receptors or like second-stage, opponent mechanisms. Predictions derived from these hypotheses do not predict the outcome of the experiments as well as the traditional notion that induced colors are in the direction complementary to the inducing color with respect to the test color. We conclude that simultaneous contrast is a consequence of interaction within higher-level chromatic mechanisms.

Higher order color mechanisms.

Evidence supporting the existence of higher order color mechanisms, that is, ones beyond the previously identified second stage mechanisms is presented. This evidence includes a reanalysis of the data of Krauskopf et al. [Vision Res. 20, 1123-1131 (1982)] on the desensitizing effects of viewing chromatically modulated fields, new experiments on a generalized version of the "transient tritanopia" experiment of Mollon and Polden [Phil. Trans. R. Soc. Lond. 278, 207-240 (1977)] and results on the relationship between discrimination and detection of brief color changes.

Temporal frequency discrimination above threshold.

Temporal frequency discrimination was measured above threshold with a two-alternative spatial forced-choice procedure. Stimuli were two 1 deg homogeneous fields modulated around a mean luminance of 3.7 log trolands. Observers determined which of the two stimuli was modulated at a higher frequency. To avoid differences in apparent modulation depth as a cue for discrimination, all stimuli were matched in apparent modulation depth to an 11 Hz standard that was 0.5 log units above its threshold. Adaptation, caused by repeated presentation of suprathreshold stimuli, was avoided by using a 15 sec inter-trial interval. The relative difference thresholds (delta f/f) were a non-monotonic function of frequency. Discrimination was best near 1.5, 4.0 and 30.0 Hz (delta f/f = 0.08) and worst near 20.0 Hz (delta f/f = 0.50). Control experiments showed that the improvement in discrimination beyond 20.0 Hz was not an artifact of mismatches in apparent modulation depth. These results demonstrate the existence of multiple channels sensitive to different ranges of temporal frequency.

A three channel model of temporal frequency perception.

This paper derives the constraints on a set of channels that would be consistent with the results of several experiments on the temporal properties of the visual system, and it describes a specific set of channels that meet these constraints. Data on simultaneous detection and discrimination require a minimum of three channels. Temporal frequency discrimination at and above threshold constrain the bandwidths and locations of the channels. The shape of the temporal modulation sensitivity function constrains their sensitivities. The functions that meet these constraints are similar to those derived from masking data, and they can account for data on flicker matching, notch losses in modulation sensitivity, and changes of perceived temporal frequency with changes of modulation depth.

Binocular flicker appears faster than monocular flicker.

Observers adjusted the frequency of an auditory click to match the apparent flicker rate of a sinusoidally modulated visual display. Matches made for binocularly viewed flicker were nearly twice those for monocularly viewed flicker but only at high rates of temporal modulation.