Bilateral Superiority in Detecting Gabor Targets Among Gabor Distracters

1. Bilateral: Distracters Absent Unilateral: Distracters Absent Bilateral: Distracters Present Unilateral: Distracters Present Attentional Cue Stimuli Noise Masks Response Prompts • 1. Which Letter? • 2. Target Present? • Yes (y) • Or • No (n) m m m m m Bilateral Superiority in Detecting Gabor Targets Among Gabor Distracters Poster # 23.407 Abstract # 773 Nestor Matthews Department of Psychology, Denison University, Granville OH 43023 USA Discussion Introduction General Method Across the four experiments, independent groups showed distracter-induced BSE’s in detection. The effect had modest spatial frequency dependence, but no orientation dependence. Distracter-induced BSE’s in detection may reflect neural events that occur earlier in the visual pathway than do those that generate distracter-induced BSE’s in motion tracking1 and orientation discrimination2,3. Although the present method did not include standard ‘litmus tests’ for visual crowding4,5, the results are more consistent with masking (specifically, surround suppression5) than with crowding because detection was impaired6, and because the distracter effects were stronger for vertical than for horizontal configurations7. Lastly, although there is fMRI evidence for two spotlights of attention within and across cortical hemispheres8, the present data are consistent with separate capacity-limited pools of resources within each cortical hemisphere –even for the fundamental visual task of detection. Stimulus Sequence On Each Trial Laterality & Distracter Conditions It has long been known that for a given point of visual fixation, the left visual field projects to the right cortical hemisphere while the right visual field projects to the left cortical hemisphere. Recent research has shown that performance on a motion tracking task is twice as good when the stimuli are distributed across both visual hemi-fields than when the stimuli are restricted to just one hemi-field, i.e., project to just one cortical hemisphere1. (It is as if the unilaterally presented stimuli “flood the cortex’s zone defense”.) Even more recently, distracter-induced bilateral superiority effects (BSE’s) have been observed on rudimentary orientation discrimination tasks2,3. The present study was conducted to determine whether distracter-induced BSE’s occur for the most basic visual task – detection. Each trial began with attentional cues marking the potential positions of Gabor targets (SF=1.3 c.p.d., size=3x3 deg window, eccentricity=14.4 deg to nearest edge, 90% contrast, duration=183 msec), which were present with 50% probability. Participants identified a central letter to ensure fixation before indicating whether a target was present or not. Across trials, bilateral and unilateral cues were randomly interleaved, as were Gabor distracters positioned between the target locations. Stimulus variations were examined across four experiments to determine which distracter-features most reliably generate BSE’s in visual detection. Results Experiment 1: Two Targets versus One Target Experiment 2: Spatial Frequency Effects * * * * Laterality Effects: High SF Target High SF Distracter F(1,19)=8.07, p=0.010, partial h2=0.298 Low SF Distracter F(1,19)=3.21, p=0.089, partial h2=0.145 Distracter Absent F(1,19)=1.36, p=0.257, partial h2=0.067 Laterality Effects: Low SF Target Low SF Distracter F(1,19)=20.04, p<0.001, partial h2=0.513 High SF Distracter F(1,19)=7.89, p=0.011, partial h2=0.294 Distracter Absent F(1,19)=4.78, p=0.041, partial h2=0.201 Laterality Effects: Two Targets Distracter Absent F(1,23)=1.29, p=0.268, partial h2=0.053 Distracter Present F(1,23)=23.26, p<0.001, partial h2=0.503 Laterality Effects: One Target Distracter Absent F(1,23)=1.73, p<0.201, partial h2=0.070 Distracter Present F(1,23)=21.80, p<0.001, partial h2=0.487 Experiment 3: Orientation Effects Experiment 4: Striped versus Solid Distracters References 1. Alvarez & Cavanagh (2005). Psychol Sci. PMID: 16102067 2. Chakravarthi & Cavanagh (2006). VSS Abstracts. # 1216, p. 274 3. Matthews & Cox(2007). VSS Abstracts. # 689, p. 180 4. Levi (2008). Vision Research. PMID: 18226828. 5. Petrov, Popple, & McKee (2007). Journal of Vision. PMID: 18217827 6. Pelli, Palomares, & Majaj (2004). Journal of Vision. PMID: 15669917 7. Feng, Jiang, & He (2007). Journal of Vision. PMID: 18217828 8. McMains & Sommers (2004). Neuron. PMID: 15157427 * * * * * * * * Laterality Effects: Oblique Target Distracter Absent F(1,14)=1.20, p=0.291, partial h2=0.079 Random Orientation F(1,14)=8.34, p=0.012, partial h2=0.373 Target Orientation F(1,14)=5.34, p=0.037, partial h2=0.276 Laterality Effects: Cardinal Target Distracter Absent F(1,14)=0.82, p=0.381, partial h2=0.055 Orthogonal Configuration F(1,14)=12.16, p=0.004, partial h2=0.465 Parallel Configuration F(1,14)=17.41, p=0.001, partial h2=0.554 Laterality Effects: Oblique Target Distracter Absent F(1,39)=1.00, p=0.323, partial h2=0.025 Gabor F(1,39)=17.97, p<0.001, partial h2=0.315 Bulls-eye F(1,39)=18.55, p<0.001, partial h2=0.322 Laterality Effects: Solid Distracters Mixed Polarity F(1,39)=5.60, p=0.023, partial h2=0.126 All White F(1,39)=2.50, p=0.126, partial h2=0.060 Chromatic F(1,39)=1.22, p=0.275, partial h2=0.030 http://www.denison.edu/~matthewsn/bilateralsuperiorityvss2008.html