Abstract
Saccades to locations at which stimuli have just disappeared manifest the encoding of these stimuli in visual short-term memory (VSTM). This saccadic selection effect is robust to visual interference but vanishes within 1 s of stimulus disappearance. As previous studies have used categorical stimulus reports, we speculated that memory representations transition from analogue to categorical formats and that only the former is susceptible to saccadic selection. Here, we examined the time course of saccadic selection in VSTM using analogue reports to understand its consequences for VSTM representations. Participants reported the orientation of a memorized stimulus either relative to vertical (clockwise vs counterclockwise; categorical trials) or by reproducing the orientation using a rotation knob (analogue trials), in separate and randomly interleaved blocks. On each trial, we flashed two randomly selected orientations at two of eight equally eccentric locations for 100 ms. Following a delay of 100, 400, or 1600 ms, a movement cue prompted a saccade to one of the two locations. Finally, a response cue probed either location, asking participants to report the corresponding orientation. In both categorical and analogue trials, we replicated the saccadic selection effect, yet contrary to previous findings, congruency with the saccade target affected memory performance across all movement-cue delays. We modeled analogue orientation reports as a combination of previously reported influences on orientation memory. The best fitting model featured the proportion and precision of target reports, an oblique effect, and a cardinal-orientation bias. The model parameters suggest that saccades increased the proportion of guesses at incongruent locations. This detrimental influence decreased with increasing movement-cue delays. These findings demonstrate that saccades cause an immediate forgetting of stimuli at saccade-incongruent locations. The similar time course in categorical and analogue trials suggests that memory representations undergo similar transitions during memory consolidation irrespective of the report type.
Acknowledgement: DFG research grant to S.O. and M.R. (OH 274/2-1 and RO 3579/6-1).