Central JSM Ophthalmology Cite this article: Foutch BK, Peck CK (2013) Gender Differences in Contrast Thresholds to Biased Stimuli. JSM Ophthalmol 1: 1007. *Corresponding author Brian K. Foutch, Rosenberg School of Optometry, University of the Incarnate Word, 9725 Datapoint Drive, San Antonio, TX 78229, Tel: 210-930-8162; E-mail: foutch@uiwtx.edu Submitted: 09 August 2013 Accepted: 22 August 2013 Published: 27 August 2013 Copyright © 2013 Foutch BK, et al. OPEN ACCESS Review Article Gender Differences in Contrast Thresholds to Biased Stimuli Brian K. Foutch 1 * and Carol K. Peck 2 1 Rosenberg School of Optometry, University of the Incarnate Word, USA 2 University of Missouri,St Louis College of Optometry, USA INTRODUCTION In humans and other primates, physiological and behavioral evidence indicates two anatomically and functionally distinct pathways originating in the magnocellular (MC) and parvocellular (PC) retinal ganglion cells [1,2]. Neurons in the MC pathway are more sensitive to object location, movement, low spatial frequency and global analysis of visual scenes. Neurons in the PC pathway are thought to be more involved with object and pattern recognition as well as color (in particular, red-green) opponency [3,4]. Although previous studies of gender effects on visual processing are heterogeneous, as a group they suggest the possibility of sexual dimorphism in parallel visual processing [5]. For example, Kramer et al. found that, in describing large shapes made up of smaller geometrical elements, boys rely more on the overall shape [6]. Girls, however, are more detailed in their descriptions, referring to the smaller shapes to describe the figures. In free drawings of imagined environmental scenes, boys tend to describe more motion and include more mechanical descriptions while girls tend to use more color [7]. In a study designed to determine the effects of gender and age on dynamic visual acuity, Ishigaki and Miyao found that men tended to detect a small gap at faster drifting rates than do women [8]. The results of these studies suggest that men may rely more on MC processing, while women may rely more on PC processing. The purpose of this work is two-fold. First, we present a limited review of the literature on gender differences in visual processing. Our second purpose is to add evidence to that body of literature, reporting the results of an experiment that examined gender differences in responses to stimulus conditions favoring MC and PC processing. In our experiment, we measured contrast thresholds and mean reaction times to two grating stimuli, one designed to be processed more strongly by MC pathways and the other by PC pathways. We predicted that women would be more sensitive to the PC-biased stimulus. MATERIALS AND METHODS Subjects were eligible if they were between 18 and 45 years old, reported a complete eye examination within the last twelve months, had best-corrected visual acuity of 20/20 or better in each eye, and had normal color vision when tested with psuedoisochromatic plates. The institutional review board of the University of Missouri – St. Louis approved the experimental protocol, and informed consent was obtained from each participant. Twenty-four adults (fifteen women, nine men) participated in the experiment. Three potential participants self-reported a history of corneal refractive surgery and were excluded from participating based on the reported effects of refractive surgery on the contrast sensitivity function [9,10]. Vision Works 4.0 Contrast Sensitivity Software (Vision Research Graphics, Durham, NH) was used to generate and display stimuli on a 21” RGB analog monitor (FlexScanF750i, Eizo Nanao Technologies Inc., Cypress, CA) located 250 cm from the observer. Monocular contrast thresholds were obtained using a QUEST modified staircase algorithm [11]. Contrast thresholds as well as mean reaction times for all positive (yes) responses were analyzed for main effects of gender by repeated-measures analysis of variance (ANOVA). All analyses were performed using SPSS statistical software (SPSS Inc., Chicago, IL).The MC-biased stimulus was a rectangular, one cycle per degree (cpd) achromatic (black and white) grating subtending three (high) by five (wide) Keywords • Gender • Parvocellular • Magnocellular • Contrast sensitivity • Reaction times Abstract We present a limited review of the literature on gender differences in visual processing. We then add evidence to that body of literature, reporting the results of an examination of gender differences in response to stimulus conditions favoring magnocellular (MC) and parvocellualr (PC) processing. We measured contrast thresholds and mean reaction times of 24 subjects (15 women, 9 men) to two grating stimuli, one designed to be processed more strongly by MC pathways and the other by PC pathways. There was a significant interaction of gender and stimulus type on contrast thresholds (F = 4.80, p = 0.03) and reaction times (F = 4.13, p = 0.04). Women were more sensitive than men to the PC-biased stimulus (t = 1.94, p = 0.05), but men and women were equally sensitive to the MC-biased stimulus (t = -1.22, p = 0.23). The results of this experiment add to the body of evidence that women may rely more on parvocellular visual processes than men.