Unmasking saccadic uncrowding

Abstract

Stimuli that are briefly presented around the time of saccades are often perceived with spatiotemporal distortions. These distortions do not always have deleterious effects on the visibility and identification of a stimulus. Recent studies reported that when a stimulus is the target of an intended saccade, it is released from both masking (De Pisapia, Kaunitz, & Melcher, 2010) and crowding (Harrison, Mattingley, & Remington, 2013). Here, we investigated pre-saccadic changes in single and crowded letter recognition performance in the absence (Experiment 1) and the presence (Experiment 2) of backward masks to determine the extent to which saccadic “uncrowding” and “unmasking” mechanisms are similar. Our results show that pre-saccadic improvements in letter recognition performance are mostly due to the presence of masks and/or stimulus transients which occur after the target is presented. More importantly, we did not find any decrease in crowding strength before impending saccades. A simplified version of a dual-channel neural model, originally proposed to explain masking phenomena, with several saccadic add-on mechanisms, could account for our results in Experiment 1. However, this model falls short in explaining how saccades drastically reduced the effect of backward masking (Experiment 2). The addition of a remapping mechanism that alters the relative spatial positions of stimuli was needed to fully account for the improvements observed when backward masks followed the letter stimuli. Taken together, our results (i) are inconsistent with saccadic uncrowding, (ii) strongly support saccadic unmasking, and (iii) suggest that pre-saccadic letter recognition is modulated by multiple perisaccadic mechanisms with different time courses.

Interaction between stimulus contrast and pre-saccadic crowding

“…[60]Agaoglu et al . [37]This studystimulus typetarget: tilted Gabor (2 cpd)target: facesupright faces for both the target and flankerstarget: letters (L, H, T, or N)target: tilted Gabor (2 cpd)flankers: 4 vertical Gabors (2 radial, 2 tangential)flankers: 2 upside down faces (Exp. 1), 4 upside down faces (Exp.…”

“…To prove that saccadic uncrowding is not a genuine effect, one needs to directly compare pre-saccadic crowding with and without masks to fully test the effect of the masks, as in a previous study of ours [37]. In that study, we asked observers to report the identity of a target letter in a letter trigram after making a saccade toward the target letter.…”

“…We think that this is highly unlikely given the absence of such an effect in this study and in Agaoglu et al . [37] where we used Gabors and letters, respectively. However, faces might be affected differently by pre-saccadic mechanisms due to their level of processing in the brain.…”

“…There are conflicting reports as to whether impending saccades release crowding of the saccade target [36,37]. Harrison et al .…”

“…As proposed by van Koningsbruggen & Buonocore [38] (see also [39]), this effect might be due to ‘saccadic unmasking’ where the effect of a forward or backward mask is reduced before saccadic eye movements [40,41]. Recently, we used letter stimuli and directly tested the effect of backward masks in addition to flankers on pre-saccadic letter recognition [37]. We found pre-saccadic improvements in performance when the target letter was crowded and masked; however, as similar improvements were also present when the target letter was only masked (but not crowded), crowding strength itself remained unchanged before saccades compared to fixation.…”