[Analysis of the eye movement patterns in visual search tasks: effect of familiarity and stimulus features].
OBJECTIVE
To analyze eye movements in asymmetric visual search using the task of normal and mirrored position letters. To evaluate the effect of familiarity and stimulus features.


METHODS
Eighty-three university students with normal or corrected-to-normal vision were asked to search for a letter in inverted position to the letters in a group of either normal or mirrored letters. Four types of letters were used (Z, N, E and G) and the eye movements were tracked by a specialized computer-based system (eyetracking). The analyzed measurements were: reaction time, fixation number and duration, saccade distance and duration.


RESULTS
All measures varied with the type of letter. Reaction time, fixation number, and saccade distance were higher when the task was to find the normal letter in a group of mirrored letters. In this condition, fixation duration was smaller. Interaction was found between familiarity and the type of letter for the reaction time, fixation number and duration. The reaction time and fixation number increased together with the stimulus complexity, with a greater increase for the normal letter target. Fixation duration, however, decreased with the complexity of the stimuli and the search condition.


CONCLUSIONS
Finding a mirrored letter among normal letters proved to be easier than the contrary. The letter type also affected the performance. When the context is formed of unfamiliar complex stimuli, the fixation duration is shorter, indicating a narrower span for visual processing. Therefore, a greater number of fixations with shorter duration are needed for the unfamiliar context while less fixations with greater duration are needed for the familiar context.
Macedo
Elizeu Coutinho de
EC
Universidade Presbiteriana Mackenzie, São Paulo, SP, Brazil. elizeumacedo@uol.com.br
Covre
Priscila
P
Orsati
Fernanda Tebexreni
FT
Oliveira
Maira Okada de
MO
Schwartzman
José Salomão
JS
D000328:Adult; D000704:Analysis of Variance; D005133:Eye Movements / Q000502:physiology*; D005260:Female; D005403:Fixation, Ocular / Q000502:physiology; D006801:Humans; D008297:Male; D010364:Pattern Recognition, Visual; D010775:Photic Stimulation / Q000379:methods*; D011930:Reaction Time / Q000502:physiology*