Load Theory of attention suggests that high perceptual load in a task leads to reduced sensory visual cortex response to task-unrelated stimuli resulting in “load-induced blindness” [e.g., Lavie, N. Attention, distraction and cognitive control under load. Current Directions in Psychological Science, 19, 143–148, 2010; Lavie, N. Distracted and confused?: Selective attention under load. Trends in Cognitive Sciences, 9, 75–82, 2005]. Consideration of the findings that visual STM (VSTM) involves sensory recruitment [e.g., Pasternak, T., & Greenlee, M. Working memory in primate sensory systems. Nature Reviews Neuroscience, 6, 97–107, 2005] within Load Theory led us to a new hypothesis regarding the effects of VSTM load on visual processing. If VSTM load draws on sensory visual capacity, then similar to perceptual load, high VSTM load should also reduce visual cortex response to incoming stimuli leading to a failure to detect them. We tested this hypothesis with fMRI and behavioral measures of visual detection sensitivity. Participants detected the presence of a contrast increment during the maintenance delay in a VSTM task requiring maintenance of color and position. Increased VSTM load (manipulated by increased set size) led to reduced retinotopic visual cortex (V1–V3) responses to contrast as well as reduced detection sensitivity, as we predicted. Additional visual detection experiments established a clear tradeoff between the amount of information maintained in VSTM and detection sensitivity, while ruling out alternative accounts for the effects of VSTM load in terms of differential spatial allocation strategies or task difficulty. These findings extend Load Theory to demonstrate a new form of competitive interactions between early visual cortex processing and visual representations held in memory under load and provide a novel line of support for the sensory recruitment hypothesis of VSTM.

Much behavioral research has shown that the presence of a unique singleton distractor during a task of visual search will typically capture attention and thus disrupt target search. Here we examined the neural correlates of such attentional capture using functional magnetic resonance imaging in human subjects during performance of a visual search task. The presence (vs. absence) of a salient yet irrelevant color singleton distractor was associated with activity in the superior parietal cortex and frontal cortex. These findings imply that the singleton distractor induced spatial shifts of attention despite its irrelevance, as predicted from an AC account. Moreover, behavioral interference by singleton distractors was strongly and negatively correlated with frontal activity. These findings provide direct evidence that the frontal cortex is involved in control of interference from irrelevant but attention-capturing distractors.

Neglect is known to produce a bias towards the ipsilesional side. Here we examined whether this bias is automatic or can be modulated by manipulating perceptual load in a relevant task [e.g., Lavie, N. (1995). Perceptual load as a necessary condition for selective attention. Journal of Experimental Psychology: Human Perception and Performance, 21 , 451–468]. Three patients with left neglect and three healthy controls made speeded choice responses to a target letter in the center of the display while attempting to ignore an irrelevant distractor presented on left or right. Perceptual load was manipulated by inducing a search for the target that appeared with another central stimulus, which was either a blob (low load) or a nontarget letter (higher load). Response competition effects from ipsilesional distractors were significantly reduced by higher load. The same increase of load, however, did not decrease distractor effects in the control group, as expected [e.g., Lavie, N., & Cox, S. (1997). On the efficiency of attentional selection: Efficient visual search results in inefficient rejection of distraction. Psychological Science, 8 , 395-398]. These results demonstrate that ipsilesional bias in neglect is not fully automated and emphasize an additional restriction of perceptual capacity. Moreover, they supported our prediction that reduced perceptual capacity in neglect can lead to improved distractor rejection with just small increases in perceptual load.