Abstract
Recent research has sought to determine if visual working memory (VWM) representations are subject to the same limitations as perceptual representations. Harrison & Bays (JNeurosci, 2018) and Yörük & Tamber-Rosenau (OPAM, 2019) investigated whether, like simultaneously presented perceptual items, VWM representations of sequentially-presented memoranda exhibit radial/tangential crowding anisotropy. No anisotropy was observed. However, a previous study using simultaneously-presented items did find additional crowding effects in VWM over and above those observed in perception (Tamber-Rosenau, Fintzi & Marois, PsychSci, 2015). It is possible that these discrepant results stem from a difference between simultaneous and sequential stimuli; specifically, the sequential paradigm is more complicated and might lead to order effects that, if not taken into account, could affect conclusions. Previous VWM studies with sequential paradigms that analyzed order found crowding in sequential presentations, but more ambiguous effects of order (Ahmad et al., SciRep, 2017, their Experiment 5), or they did not report order effects (Harrison & Bays, 2018). Here, we reanalyzed the Yörük & Tamber-Rosenau (2019) data with additional data collected since, as well as the Harrison and Bays (2018) data. In both cases, we found significant order effects in which errors diminished from the first to last item. This is consistent with a previous study showing that VWM representations shift from occipital visual cortex to parietal and frontal brain areas with delay and presentation of additional memoranda (Vergauwe et al., Psychonomics, 2019). It also accords with the finding that occipital, but not parietal, VWM representations are modulated by the presence of distractors during VWM maintenance (Bettencourt & Xu, NatNeurosci, 2016). Therefore, care should be taken in interpreting the presence/absence or quality of cross-item interactions such as crowding in sequentially-presented VWM arrays because these arrays may reflect storage of different items in distinct VWM states or representations.