Crowding or Surround Suppression with a Hybrid Stimulus-Task Combination?

Abstract

Both crowding and surround suppression result in fuzzy visual patterns, yet they have been treated as different phenomena because they vary in some properties. For example, an inward-outward asymmetry of masking is a hallmark of crowding but does not appear in surround suppression. Studies on surround suppression and crowding usually employ different stimulus patterns and tasks, and it is unclear whether the discrepancies between them derive from the different stimulus patterns, the different tasks, or whether they are just different phenomena. A hybrid of stimulus pattern (large surround annuli, usually used in surround suppression) and task (discrimination task, usually used in crowding studies) was used in a fine orientation discrimination task, with the inward-outward asymmetry as a “critical test” indicator. The results showed that whereas some observers showed no inward-outward asymmetry, others showed such an asymmetry. Intriguingly, this asymmetry was in the direction opposite to that commonly reported. Together, the results cannot be wholly predicted by either surround suppression or crowding, and might reveal a new mechanism because of our particular combination of task and stimulus pattern.