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Daryl Fougnie, James J. Todd, René Marois; Visual short-term memory load induces inattentional blindness. Journal of Vision 2005;5(8):545. doi: 10.1167/5.8.545.
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We have recently shown diametrically opposite effects of visual short-term memory (VSTM) load onto brain activity in two distinct regions of the parietal cortex: While posterior parietal/superior occipital cortex activity increases with VSTM load (Todd & Marois, 2004), the temporal-parietal junction (TPJ) is increasingly suppressed (Todd et al., submitted). Since the TPJ is a key neural substrate for stimulus-driven attention, we hypothesized that TPJ suppression with increased VSTM load should also impair the detection of novel, unexpected visual events. We tested this hypothesis using an inattentional blindness paradigm to measure detection performance for an unexpected salient stimulus while attention was engaged in a primary VSTM task. Subjects memorized the color and position of a set of discs and, following a 5s retention interval, determined whether a single disc presented in a probe display matched in location and color one of the discs in the sample display. The load of the VSTM task was manipulated between two groups of 38 subjects (Low load: 1 object, High load: 4 objects). We measured subjects' performance in detecting an unexpected, novel stimulus appearing in the periphery of the visual field during the retention period of the VSTM task. Far more subjects failed to detect the critical stimulus under High VSTM load than Low VSTM load (Fisher's exact test, p =.007). By contrast, almost all subjects detected the critical stimulus when the VSTM task was ignored, indicating that the stimulus was easily perceived under full attention. These results support the hypothesis that VSTM load suppresses the neural circuit for explicit perception of unexpected, salient stimuli.
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