Purchase this article with an account.
Rufin VanRullen, Thomas Carlson, Patrick Cavanagh; Dividing attention between multiple targets: simultaneous or sequential allocation?. Journal of Vision 2007;7(9):642. doi: 10.1167/7.9.642.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Increasing evidence suggests that attention can concurrently select multiple locations; yet it is not clear whether this ability relies on continuous allocation of attention to the different targets (a “parallel” strategy), or whether attention switches rapidly between the targets (a temporal “sampling” strategy). Indeed, both strategies can explain the occurrence of classic “set size effects” (i.e. decreases of performance with increasing number of attended items), either because attention is a limited resource (“parallel” strategy), or because the effective time that attention samples each object decreases when several objects must be attended (“sampling” strategy). However, the psychometric function for detection of a single target as a function of its duration can be used to predict the expected psychometric function for multiple targets, and the predicted shape is quite different for parallel and sequential strategies. We find that the model that best predicts our observed data is a “sampling” model when the task involves a challenging contrast decrement detection (with the sampling period around 140ms, ranging from 100ms to 180ms across our 8 subjects), whereas the optimal model is a “parallel” one for an easy version of the same task (with a performance loss of 16% for each additional item to be attended). This distinction was observed for all subjects tested. The two versions of the task give rise, respectively, to serial (40ms/item) and parallel (0ms/item) slopes in a visual search situation. The results suggest that, at least for attentionally demanding tasks, it may not be possible to simultaneously attend to multiple locations; instead, the multiple items of interest are processed in series at a rate of about 7 items per second.
This PDF is available to Subscribers Only