Eye movements are not optimal: People simply employ reasonable but idiosyncratic search strategies
Bobby Glenn Stuijfzand, Roland Baddeley, William J. Browne · 2015
The ideal searcher framework postulates that during visual search the observer directs attention in order to maximise knowledge on a target’s location, taking into account retinal sensitivity. As the human visual field maintains high resolution further horizontally than vertically an implication is that humans are likely to exhibit many short eye-movements in an approximately horizontal direction and then make an occasional jump vertically. This particular behaviour has been observed previously in a visual search task by Najemnik and Geisler (2005, 2008). We tested this hypothesis by repeating their search task, and, as their data was based on two participants, we increased the number of participants in order to assess whether this behaviour is a general strategy across participants. We took a novel analytical approach by using Hidden Markov Models, allowing for the identification of clusters (i.e., horizontal short saccades and vertical long saccades) in the data, as well as the transitions between clusters. Results however showed the two expected clusters could not be identified from the full dataset. Rather we found that strategies vary across participants. Based on these results we theorise that reinforcement may have influenced the predominance of particular eye-movements. We present some initial results investigating this hypothesis.