The information limits of saccadic targeting: How much guidance is there in eye movements during search?
Several human studies have measured the accuracy of the first saccade during visual search to determine whether the first saccade is guided by visual information about the target or whether it follows some pre-programmed or arbitrary scan path. However, different studies have found disparate results (Williams, 1966, 1967; Zelinski, 1996; Findlay, 1997).  Rather than focusing on the binary question of whether the first saccade is guided or not, I have quantified the amount of information used by the saccadic system for the first saccade of search.  I’ve compared human saccade to the best-possible performance, the ideal observer (efficiency of the fist saccade = 6%-20%).  I’ve similarly measured the relative efficiency of the accuracy of the first saccade with respect to the final perceptual decision (70-90 %).  Our results showed that relative efficiency of the first saccade increases with target saliency (signal to noise ratio; Perception, accepted). 

Is the amount of information available to the first saccade the same as that available to a perceptual decision at the time of saccadic programming?
Recent work by physiologists has shown that there are areas in the Frontal Eye Field that encode saliency information about targets to be fixated (saccadic targeting; Schall et al, 1995; Bichot et al, 1996).  Physiologists have wondered whether the information encoded in the Front Eye Field mirrors information encoded in the visual cortical areas (e.g. V1, V2, etc) or whether it corresponds to a separate independent coding pathway. 
We have conducted experiments where we compared the accuracy of the first saccade to the accuracy of a perceptual decision in a condition where the display is briefly flashed for a time approximately similar to the time of saccadic programming. The time of saccadic programming is estimated to be approximately 70-100 ms less than the saccade latency.   Our results show that there is little difference between the amount of information available to the first saccade and that available to the perceptual system at the time of saccadic programming. These results might suggest that the Frontal Eye Field has access to the same amount of information as that encoded in cortical areas and used for perceptual decisions. 

Does the second saccade during search have access to more information about target location than the first saccade?
We have compared performance of the human second saccade during visual with respect to the second saccade of the an ideal observer constrained to the information of the human first saccade. This contrained ideal observer represents an upper bound on performance of an observer that does not have an increase in the amount or quality of target location information from the 1st to the second saccade. Our results show that human performance of the second saccade during search exceeded an ideal observer constrained to use the same information used by the observers’ first saccade. Our data therefore suggest that the human second search saccade is based on more/better information than was the first (ARVO, 2000, ECVP, 2000).

Selected Publications:

Beutter, B.R., Eckstein, M.P., Stone, L.S., Perceptual and saccadic decisions in visual search I. Detection and contrast discrimination, Journal of the Optical Society of America A, (2003) In press.

Murray, R.., Beutter, B.R., Eckstein, M.P., Stone, L.S., Perceptual and saccadic decisions in visual search II. Letter discrimination, Journal of the Optical Society of America A, (2003) In press.

Eckstein, M.P., Beutter, B.R., Stone, L.S., Quantifying the performance limits of human saccadic targeting in visual search, Perception , 30, 1389-1401, (2001)

Eckstein, M.P., Beutter, B.R., Stone, L., The effect of set-size on the relation between saccadic and perceptual decisions during search, Investigative Ophthalmology & Visual Science (Suppl.), 39, 1031, (1998) 

M.P. Eckstein, L.S., Stone, B. R. Beutter, The accuracy of saccadic and perceptual decisions in visual search ,  Perception (Suppl.), 26, 70, (1997) 

Eckstein, M.P., Stone, L.S., Beutter, B.R.  The visual efficiency of eye movements during search. Investigative Ophthalmology & Visual Science (1997).