Visuospatial working memory mediates inhibitory and facilitatory guidance in preview search

Visual search is faster and more accurate when a subset of distractors is presented before the display containing the target. This “preview benefit” has been attributed to separate inhibitory and facilitatory guidance mechanisms during search. In the preview task the temporal cues thought to elicit inhibition and facilitation provide complementary sources of information about the likely location of the target. In this study, we use a Bayesian Observer model to compare sensitivity when the temporal cues eliciting inhibition and facilitation produce complementary, and competing, sources of information. Observers searched for T-shaped targets among L-shaped distractors in two standard and two preview conditions. In the standard conditions, all the objects in the display appeared at the same time. In the preview conditions, the initial subset of distractors either stayed on the screen or disappeared before the onset of the search display, which contained the target when present. In the latter, the synchronous onset of old and new objects negates the predictive utility of stimulus-driven capture during search. The results indicate observers combine memory-driven inhibition and sensory-driven capture to reduce spatial uncertainty about the target’s likely location during search. In the absence of spatially predictive onsets, memory-driven inhibition at old locations persists despite irrelevant sensory change at previewed locations. This result is consistent with a bias towards unattended objects during search via the active suppression of irrelevant capture at previously attended locations

Costs in searching for two targets: dividing search across target types could improve airport security screening

The cost of searching for two visual targets simultaneously was compared against two separate single-target searches using exposure time and accuracy measures within a staircase procedure. Dual-target search for all stimuli (colour, shape and orientation) exhibited a loss of accuracy for one target. For orientation and shape, this dual-target cost in accuracy was extreme, with chance-level performance on one target. For colour, dual-target search exhibited an additional cost in search time, with search requiring a longer exposure than the summed time required for two single-target searches. An additional search-time cost was also found for orientation targets when irrelevant colour variation was added to the display. In conclusion, dual-target search for dissimilar targets is accompanied by an accuracy cost. Furthermore, colour variation, whether task-relevant or not, leads to an additional cost in processing speed. The results suggest that a divided-effort strategy would improve performance in search tasks such as X-ray baggage screening

Search efficiency for multiple targets

In most visual search experiments, there is only one possible target object or class of objects. The experiment reported here compares performance in these single-target searches against performance when the target can be either of two different stimuli. The targets used in this experiment were color squares. Results showed that conducting two single-target searches is more efficient than carrying out a dual target search. If visual search is driven by a mental template of the object to be found, then searches for two targets may require a very general template, or a pair of templates that are active simultaneously, which apparently produces less efficient search. Many real world search tasks, such as searches of X-ray images by baggage screeners, require simultaneous search for very different targets (“Find any guns or knives or explosive devices.”). This need for generality could result in search that is less directed and therefore less efficient