Transient and sustained masking

The detection threshold of a brief test stimulus was measured as a function of the onset asynchrony between it and a long-lasting suprathreshold masking stimulus. Both stimuli were sine-wave gratings of the same vertical orientation and in the peak-subtract phase but differed in spatial frequency by a factor of 3. The temporal masking functions obtained with 2- and 6-cycles/deg maskers of high contrast exhibited transient on- and off-peaks of masking and a sustained effect during the masker exposure. An 18-cycles/deg masker caused sustained masking only. Experiments with maskers of variable spatial frequency and contrast showed that, in the low-spatial-frequency range, the mechanism responsible for the transient effect was more sensitive than that generating the sustained effect, while the sustained effect required less contrast in the high-spatial-frequency range. The results are considered as evidence, in addition to previous findings, for the sustained/transient dichotomy in the temporal domain.