Facilitation and masking of briefly presented gratings: time-course and contrast dependence.
We measured two-alternative forced-choice contrast thresholds for briefly presented sinusoidal gratings in the presence of superimposed masking gratings of various contrasts, and at a range of onset asynchronies. Facilitation (lower thresholds) occurred when the mask was simultaneous, in-phase, and near-threshold, but was abolished at asynchronies of 50 msec or more and by presenting the test grating as a brief contrast reversal instead of a pulse. We argue that facilitation requires temporal summation of responses within the same neural channels, but our results do not distinguish between transducer and uncertainty models. Masking (threshold elevation) occurred over a broader range of asynchronies, and was not abolished by test contrast reversal. Masking and facilitation probably depend on different processes with different time-courses. The occurrence of masking at asynchronies outside the range of temporal summation suggests that a static, compressive transducer does not, in general, account for masking. Brief masking and prolonged contrast adaptation are very similar in magnitude, and as a function of contrast and relative spatial frequency. Masking and adaptation may have a common origin, but differ in speed of recovery.
Georgeson
M A
MA
Department of Psychology, University of Bristol, England.
Georgeson
J M
JM
D000221:Adaptation, Ocular; D004192:Discrimination, Psychological / Q000502:physiology; D005556:Form Perception / Q000502:physiology*; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology*; D010470:Perceptual Masking / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D013997:Time Factors