On the role of X and simple cells in human contrast processing.
We investigated the potential role of retinal X and cortical simple cells in determining human psychophysical detection performance under contrast masking conditions. Since both X and simple cells exhibit a null phase, the phase of a background mask should affect the visibility of a test grating processed by such cells. Sinusoidal test gratings of either 1 or 7 c/deg were presented as a sustained or transient increment against a background mask of the same size and spatial frequency at either 0 or 90 deg phase. For background contrasts from 0.5% up to 40%, psychophysical contrast sensitivity was phase-independent for all conditions. Therefore, either (1) contrast threshold is mediated by cells with non-linear spatial summation properties, such as Y or complex cells, or (2) the masking effect of the background occurs after a phase-insensitive combination or pooling of simple cell responses in the cortex.
Lawton
T B
TB
Nano Tech Services, Channel Islands Harbor, CA 93035.
Tyler
C W
CW
D015350:Contrast Sensitivity / Q000502:physiology*; D004192:Discrimination, Psychological / Q000502:physiology; D006801:Humans; D010364:Pattern Recognition, Visual / Q000502:physiology; D010470:Perceptual Masking / Q000502:physiology; D011601:Psychophysics; D012160:Retina / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology; D014793:Visual Cortex / Q000502:physiology*