Temporal limits to the detection of correlation in transpositionally symmetric dynamic dot textures.

Abstract

Adding a delay within spatially correlated point-pairs constituting a dynamic transpositionally symmetric texture has three distinct perceptual outcomes (the specific outcome depending on the size of the delay): global pattern, coherent motion, and apparent randomness. The temporal limits for global pattern and coherent motion were measured for eight different values of the extent of transposition (.11 to .70 deg of visual angle) and for four different stimulus sizes (3,6,7, and 9 deg square),with texture density constant at the retina. Temporal limits for coherent motion varied inversely as a function of increasing spatial separation (.11 deg ≤Δ≤.42 deg), but beyond this separation (.42 deg<Δd≤.70 deg), the limit was invariant as a function of Δd (∼60 msec). The temporal limit for global pattern was independent of the size of Δd and fell at ∼60 msec, exhibiting spatiotemporal characteristics different from those for coherent motion. On the basis of this difference, it is suggested that the human visual system processes the perceptual attributes global pattern and coherent motion independently, despite their common correlational basis. Further evidence to support this proposal is provided by the finding that variations in stimulus size have no effect on the temporal limit for global pattern and have differential effects on the temporal limit for coherent motion, depending on the size of △d.