The effect of training on search for complex stimuli

Abstract

Purpose: We investigated changes in search efficiency over time for a class of complex targets defined by shape and colour. The aims were to: 1) manipulate target variation in terms of orientation and identity in order to establish the effects on learning and subsequent generalisation; 2) identify the learning conditions for training that afford efficient detection of novel objects within the target class. Method: Participants responded to the absence or presence of a target class exemplar in an eight-item display. All items were x-ray images of baggage items and the target class was guns. Four training conditions manipulated variation in target identity and orientation on each trial: (i) single exemplar of the target class, single orientation (ii) single exemplar, multiple orientations (iii) multiple exemplars, single orientation (iv) multiple exemplars, multiple orientations. Participants completed 15 training blocks of 500 trials. The impact of training was examined using five further blocks of multiple exemplar, multiple orientation trials. Performance was evaluated by exposure threshold controlled by a 3:1 staircase procedure. Results: Exposures were averaged over bins of 50 trials. Slopes of exposure against bin were log-transformed. Analysis of the linear fits showed that training under single orientation conditions produced shallower slopes than multiple orientation conditions. However, analysis of the testing phase revealed steeper slopes for those trained with single orientations than multiple orientations, indicating poorer generalisation. Conclusion: Even with complex stimuli, training can improve search efficiency. The data show that variation in orientation during training has a strong effect on efficiency of search and standard of generalisation, while the effect of variation in the target identity is less clear.

Footnotes

 The research was funded by the U.S. Transportation Security Administration. The participants were not TSA screeners, and they had not received TSA training