Beyond Bouma's window: How to explain global aspects of crowding?
Fig 10
a: Activity in the LAMINART model. Colors represent the most active orientation (red: vertical, green: horizontal). When a stimulus is presented, segmentation starts to propagate along connected (illusory or actual) contours from two locations marked by attentional selection signals. Visual elements linked together by illusory contours form a group. After dynamic, recurrent processing, the stimulus is represented by three distinct neural populations, one for each group. Crowding is high if other elements are grouped in the same population as the vernier, and low if the vernier is alone. On the left, the flanker is hard to segment because of its proximity to the vernier. Across the trials, the selection signals often overlap with the whole stimulus, considered as a single group. Therefore, the flanker interferes with the vernier in most trials, and crowding is high. On the right, the flankers are linked by illusory contours and form a group that spans a large surface. In this case, segmentation signals can easily hit the flankers group successfully (without hitting the vernier). The vernier thus ends up alone in its group in most trials and crowding is low. b: The left row shows human performance with the square flanker stimuli. The right row is the output of the LAMINART model. It fits the data very well. The same holds true for a majority of our stimuli. To compute the LAMINART’s output values, we used the same linking hypothesis as in the original description of the model [45]: template matching is used to decide if the target vernier offset is left or right, and this result is monotonically transformed into a threshold-like measure. c: Sometimes flankers group together (illusory contours are formed) when they should not, erroneously predicting uncrowding for this condition. d: Sometimes flankers group with the vernier when they should not. Here, weak illusory contours connect the central flanker and the vernier. No uncrowding can be produced for this condition because segmentation always spreads to the vernier, independently of the success of the selection signals.