Katelyn Osuna¹ (), Jason Yeatman¹, Maha Ramamurthy¹; ¹Division of Developmental Behavioral-Pediatrics, School of Medicine & Graduate School of Education, Stanford University.

Reading is a visual and linguistic task that demands the shifting and focusing of attention. While it is necessary to understand the visual dimensions to reading through ecologically relevant stimuli (letters), it is critical to know the extent of how these effects are generalizable to non-linguistic stimuli (pseudo-letters). In the current study, we ask if the effects of visual spatial attention are similar in encoding pseudo-letters. We hypothesize that if processing a string of pseudo-letters is similar to that of letters then the effects of spatial attention should also be similar and if the encoding accuracy of pseudo-letters are different then spatial attention effects could depend on accuracy at each position. We measured the effects of spatial cues in a multi-element processing task to characterize the differential effects of exogenous and endogenous covert spatial attention on various aspects of encoding unnamable element combinations and compared results to our previous work with letter strings. A string of six pseudo-letters was presented briefly (120ms). Participants (n=13) were asked to report the element at one of the post-cued positions from 12 choices. Attention was manipulated with endogenous and exogenous pre-cues. On valid trials, pre- and post-cue sides match; on invalid trials they mismatch, and on neutral trials all stimuli are pre-cued. Eyes were tracked to ensure fixation during the encoding period. We observe that overall attention effects are lower with pseudo-letters compared to letters, but exogenous effects peak at 50ms and endogenous effects peak at 600ms. The serial position function (SPF) for pseudo-letters was inverted U-shaped (less W-shaped compared to letters) with no encoding hemifield-asymmetries unlike letters with a right hemifield bias. We found that a valid endogenous pre-cue increased encoding accuracy for the crowded element position on the right hemifield by reducing transposition errors at that position.

Acknowledgements: Stanford Bio-X Undergraduate Fellowship Program