Dr. Lisa Jefferies
University of British Columbia
Friday, Nov. 16th 10-11am
Title: Temporal dynamics of attentional control: Assessing the rate of "zooming"
The vast amount of visual information in the world necessitates a selective mechanism that limits processing to objects or locations of interest. Visual attention fulfils this selective function, and may be allocated with varying degrees of success over space and time. We propose a qualitative model that accounts for the modulation of the spatial extent of the focus of attention across time, and test that model in a series of experiments. Specifically, the Attentional Blink (AB) and Lag-1 sparing were employed to test the spatiotemporal modulations of attention. When two targets are presented within a stream of distractor items, identification of the second target is impaired when it follows 100-500 ms after the first target, a phenomenon known as the attentional blink (Raymond, Shapiro & Arnell, 1992). Paradoxically, the second target is sometimes identified quite accurately when it immediately follows the first target (Lag-1 sparing; Potter et al., 1998). Lag-1 sparing always occurs when the two targets appear in the same spatial location (Visser, Bischof, & Di Lollo, 1999), but occurs with spatially separated targets only when the second target falls within the focus of attention (Jefferies et al., 2007). As such, the incidence and magnitude of Lag-1 sparing with spatially separated targets can be used to index changes in the extent of the focus of attention as a function of time. In the current research, we found a progressive, linear transition from Lag-1 sparing to AB deficit as the stimulus-onset-asynchrony (SOA) between the targets was increased. This strongly suggests that the spatial extent of the focus of attention varies linearly over time and that the expanding and shrinking of the focus of attention may be analog in nature. Additional experiments in which factors such as the spatial separation between the streams and the brightness of the targets were manipulated were also conducted, and these experiments provide further tests of the model.