Spatial integration of orientation-defined texture
63.445, Wednesday, 21-May, 8:30 am - 12:30 pm, Banyan Breezeway
Gunnar Schmidtmann1, Ben Jennings1, Jason Bell2, Frederick Kingdom1; 1McGill University, Department of Ophthalmology, Vision Research, 2The University of Western Australia, School of Psychology
Previous studies have reported linear summation for Glass patterns from measures of detection thresholds as a function of signal area, and have proposed specialized concentric orientation texture detectors (Wilkinson et al., 1997; cf. Dakin & Bex, 2002). Motivated by these findings and recent results in curvature discrimination showing strong summation of curvature information for circular segments up to 180˚ (semi-circle) (Schmidtmann et al., 2013), we investigated spatial integration for a variety of different orientation-defined textures (circular, radial, spiral, translational) composed of 150 Gabor patches. In a 2AFC, subjects had to detect the texture in a single randomly positioned pie-wedge sector of varying angular extent ranging from 36˚ - 360˚. The signal to noise ratio in that sector was varied, whereas the remaining array contained randomly oriented elements (noise only). Results show that, contrary to previous studies, detection thresholds for all texture types decrease with angular extent following a power-law function with an exponent around -0.5. To investigate the role of spatial uncertainty we fixed the angular position of the sector containing signal elements. This improved performance disproportionately for small sectors, resulting in even weaker summation across angular extent and can therefore not explain any lack of summation. Next we analyzed the correlation between correct responses and clustering of signal elements. Results show that observers are more likely to make correct responses if signal elements are clustered (high density). To summarize, we found that, a) the detection of orientation-defined texture is independent of texture type; b) summation across area was weaker than reported previously and c) summation strength is further reduced by adding spatial certainty. We suggest that detecting local clusters of signal elements might limit the detection of global form in these textures.