Differences between fovea and parafovea in visual search processes.

Visual objects that differ from the surroundings for some simple feature, e.g. colour or line orientation, or for some shape parameters ("textons", Julez, 1986) are believed to be detected in parallel from different locations in the visual field without requiring a serial search process. Tachistoscopic presentations of textures were used to compare the time course of search processes in the fovea and parafovea. Detection of targets differing for a simple feature (line orientation or line crossings) from the surrounding elements was found to have a time course typical of parallel processing for coarse textures extending into the parafovea. For fine textures confined into the fovea the time course was suggestive of a serial search process even for these textons. These findings are consistent with the hypothesis that parallel processing of lines or crossings is subserved by a coarse network of detectors with relatively large receptive field and low resolution. For the counting of coloured spots in a background of a different colour the parafovea has the same time requirements as the fovea.