EFFECTS OF CONTRAST, ECCENTRICITY AND POSITION IN THE DETECTION OF VISUAL STIMULI IN HUMANS

Introduction. Contrast, eccentricity and position of stimuli used on research of attention in human vision strongly vary among studies. Aim. To study how contrast, eccentricity and position affects detection of stimuli in humans. Subjects and methods. In adults with normal vision, we measured response times to stimuli (gray circles of 0.5 degrees of diameter) presented at random at eight polar coordinates, in three eccentricities with respect of fixation point (2.15, 3.83 and 5.53 degrees) and with three levels of contrast (6, 16 and 78%). Results. Stimuli with eccentricity of 5.38 degrees and 6% of contrast showed the longest response times. In all eccentricities studied, longer response times were found with stimuli of 6% of contrast. Response times of stimuli of 16% and 78% of contrast showed similar response times in all eccentricities studied. Response times founded at eight polar coordinates were heterogeneous at eccentricities of 2.15 and 5.53 degrees, but not at 3.83 degrees. Conclusions. Contrast is the factor that most influence detection of visual stimuli used in this study, particularly at the biggest eccentricity employed. Response times among polar coordinates are also affected by eccentricities of 2.15 and 5.53 degrees, suggesting that distance of stimuli to fixation point is critical for visual detection of stimuli. [REV NEUROL 2009; 48: 129-33]