How does the brain combine spatio-temporal signals from the two eyes? We quantified binocular summation as the improvement in 2AFC contrast sensitivity for flickering gratings seen by two eyes compared with one. Binocular gratings in-phase showed sensitivity up to 1.8 times higher, suggesting nearly linear summation of contrasts. The binocular advantage decreased to 1.4 at lower spatial and higher temporal frequencies (0.25 cycle deg-1, 30 Hz). Dichoptic, antiphase gratings showed only a small binocular advantage, by a factor of 1.1 to 1.2, but no evidence of cancellation. We present a signal-processing model to account for the contrast-sensitivity functions and the pattern of binocular summation. It has linear sustained and transient temporal filters, nonlinear transduction, and half-wave rectification that creates ON and OFF channels. Binocular summation occurs separately within ON and OFF channels, thus explaining the phase-specific binocular advantage. The model also accounts for earlier findings on detection of brief antiphase flashes and the surprising finding that dichoptic antiphase flicker is seen as frequency-doubled (Cavonius et al, 1992 Ophthalmic and Physiological Optics 12 153 - 156). [Supported by EPSRC project GR/S74515/01].
|Publication status||Published - 2007|
|Event||13th European Conference on Visual Perception - Arezzo (IT), Italy|
Duration: 27 Aug 2007 → 31 Aug 2007
|Conference||13th European Conference on Visual Perception|
|Period||27/08/07 → 31/08/07|
Bibliographical noteAbstract published in ECVP 2007 Abstract Supplement, Perception 36 (Supplement), p.60. 0001-4966.
- spatio-temporal signals
- binocular summation
- 2AFC contrast sensitivity
- flickering gratings
- binocular gratings in-phase
- contrast-sensitivity functions
- pattern of binocular summation