Abstract

Masking is defined as the change in threshold energy e_T*(τ) of a test stimulus T induced by a masking stimulus M of energy e_M as a function of the relative time τ of occurrence. Masking is maximum when T and M occur simultaneously. A slight decrease in threshold for tests preceding the masking impulse by about 0.1 sec was explained as an alteration in appearance of the subsequent masking flash by a “subthreshold” test flash. Impulse-contrast threshold e_T*/e_M was investigated for masking impulses M of seven different energies superimposed on five backgrounds B. The increases in test threshold caused by M and by B were found to be independent and a modified Weber’s law (adjusted contrast threshold C_δ*≈0.1) held approximately. This conclusion was supported in a supplementary investigation of C_δ* using a category-rating-scale method.

Impulse masking results were applied to predicting the masking peak at the onset of a long flash by treating the first 60 msec as an impulse. The lowering of thresholds of tests delayed in a long masking flash implied other detection mechanisms (e.g., temporal resolution). Theoretical predictions accounted for 94% and 97% of the variance in two relevant experiments, correctly predicting the effect of masking-flash duration and of background intensity.

In both steady and intermittent light, masking is attributed primarily to fast processes (time constant ≪1 sec) which presumably have a neural rather than a photochemical basis.

© 1965 Optical Society of America

Temporal Summation of Positive and Negative Flashes in the Visual System*

Mitsuo Ikeda
J. Opt. Soc. Am. 55(11) 1527-1534 (1965)

Temporal Summation During Backward Visual Masking*

Robert T. Kintz and Robert M. Boynton
J. Opt. Soc. Am. 59(2) 212-216 (1969)

Negative Flashes, Positive Flashes, and Flicker Examined by Increment Threshold Technique*

Mitsuo Ikeda and Robert M. Boynton
J. Opt. Soc. Am. 55(5) 560-566 (1965)

Effect of Masking by Light on the Apparent Contrast of Flashed Gratings*

Thomas R. Corwin
J. Opt. Soc. Am. 61(9) 1172-1176 (1971)

Category Judgments as Functions of Flash Luminance and Duration*

Mark F. Lewis
J. Opt. Soc. Am. 55(12) 1655-1660 (1965)