Abstract
Object recognition is greatly impaired when they are presented in clutter, especially in the visual periphery, a mechanism called crowding. Recent work discovered a related phenomenon called redundancy masking: When multiple identical items are presented in the periphery, observers often report perceiving less items than the actual number of presented items. Common measures used to study crowding, such as identification tasks, are not suited to reveal such effects as single target identification does not reveal the total number of items perceived. Here, we examined redundancy masking and the appearance of multiple identical lines in the periphery when they were grouped by color, contrast or length into different patterns. Stimuli consisted of 3-5 vertical lines, briefly presented in the periphery. In three separate experiments, we varied either colour, contrast polarity or length of the lines by using two different feature values for each manipulation. This allowed us to differently group lines within the stimulus: a uniform stimulus, a stimulus with an alternating pattern or a subgroup of identical lines with a different line at the stimulus edge. Observers reported the number of lines and their appearance, indicating the feature values of each perceived line. First, we observed redundancy masking in all conditions. Second, we found highly systematic appearance patterns across observers: Stimulus edges (outer lines), detecting the presence of the two feature values, and noticing their ratio remained intact. Redundancy-masked lines were predominantly from the center of the stimulus and from within the subgroup of identical lines. In conclusion, our results show that redundant information is compressed, but crucial information such as the edges that provide information about, for example, the size and shape of the entire stimulus remain intact. Our results highlight the importance of moving beyond simple identification tasks to address important questions in vision research.