Manipulating contour smoothness: Evidence that the association-field model underlies contour integration in the periphery

Field et al (1993 Vision Research 33 173 - 193) proposed that an association-field model (AFM) underlies performance in path-paradigm (PP) tasks. The AFM integrates dynamically the outputs of filters with different orientation preferences. In the current study, simulations were used to examine whether PP tasks could be solved by a simple-filter model (SFM). The SFM posits that 2AFC decisions are based upon the maximum length of zero-bounded regions after convolution of stimuli with elongated filters -- integration only occurs between the outputs of co-oriented filters. In contrast to Hess and Dakin (1997 Nature 390 602 - 604; 1999 Vision Research 39 947 - 959), initial simulations showed that manipulations of Gabor patch phase were an inadequate control for the contribution of the SFM towards PP performance. In a further simulation, the angular difference between neighbouring contour elements was held constant, while the global smoothness of contours was varied. The SFM favoured jagged contours and was relatively impaired in the detection of smoother contours. Conversely, human observers favoured smoother contours in the fovea and parafovea (13°). Whilst the SFM could account for the detection of jagged and randomly structured contours, it is inadequate as an account of the detection of smooth contours. Consequently, the AFM may provide a parsimonious account of contour integration across the whole visual field.