Effect of laterality-specific training on visual learning Jenna Kelly & Nestor Matthews Department of Psychology, Denison University, Granville OH USA To a large degree, visual perception is laterally specific; information from the right half of the visual field (hemifield) is processed by the left visual cortex, while information from the left hemifield is processed by the right visual cortex. Information from the two hemifields is integrated primarily through hemispheric communication via the corpus callosum. Superiority in tracking visual targets has been detected for stimuli presented bilaterally rather than unilaterally, possibly suggesting independent resources for processing within each hemifield (Alvarez & Cavanagh, 2005). A similar bilateral superiority effect has been identified on a more visually basic detection task (Reardon & Matthews, 2008). This effect may be related to a superior ability to suppress irrelevant information (Awh & Pashler, 2000). Given that stimulus-specific perceptual learning has been previously demonstrated with simple visual tasks (Ahissar & Hochstein, 1997), the current study was intended to identify whether specificity of learning would occur with laterality as a variable. We investigated whether the bilateral superiority effect is solely a capacity difference or whether there is also a difference in plasticity for bilateral and unilateral tasks. That is, is learning specific to whether training happens with bilateral or unilateral stimuli? It was predicted that participants trained bilaterally would improve only bilaterally and that those trained unilaterally would improve only unilaterally. We also sought to establish whether what appears to be bilateral superiority is actually an effect of laterality and not of orientation (horizontal/ vertical). Discussion Introduction References Range-Finder Attentional Cue m StimuliNoise Masks 1. Which Letter? 2. Target Present? Yes (y) Or No (n) Response Prompts Method Stimulus Sequence On Each Trial Results Pre-/ Post-trainingTraining Displacement Orientation * * * * Significant Range-Finder Effects Distracter Main Effect F(1,19)=76.603, p<0.001, partial  2 =0.801 Duration Main Effect F(1,19)=37.460, p<0.001, partial  2 =0.663 Laterality: Distracter, 167-ms F(1,19)=5.732, p=0.027, partial  2 =0.232 Learning: General vs. Specific Training Session F(1,19)= , p<0.001, partial  2 =0.841 Configuration (Post, No Distracter) F(1,19)=2.370, p=0.140, n.s., partial  2 =0.111 Configuration (Post, Distracter) F(1,19)=2.938, p=0.103, n.s., partial  2 =0.134 Laterality Effects: Solid Distracters Displacement Orientation*Configuration F(1,17)=8.412, p=0.010, partial  2 =0.331 Laterality F(1,17)=6.969, p=0.017, partial  2 =0.291 Distance from Vertical Meridian F(1,17)=8.412, p=0.010, partial  2 =0.331 This project was supported by a Grant-In-Aid of Research from Sigma Xi, The Scientific Research Society; an Anderson Summer Research Assistantship; and an award from the Denison University Research Foundation. Acknowledgements Training Effects Bilateral, No Distracter F(4,36)=12.374, p<0.001, partial  2 =0.579 Unilateral, No Distracter F(4,36)=10.730, p<0.001, partial  2 =0.544 Bilateral, Distracter F(4,36)=37.279, p<0.001, partial  2 =0.806 Unilateral, Distracter F(4,36)=18.606, p<0.001, partial  2 =0.674 Effects of Inverted Configurations Configuration F(1,19)=7.656, p=0.012, partial  2 =0.287 Distracter F(1,19)=14.945, p=0.001, partial  2 =0.440 Interaction F(1,19)=0.177, p=0.678, n.s., partial  2 =0.009 Letter DurationTarget/Distracter Inversion Ahissar, M., and Hochstein, S. (1997). Task difficulty and the specificity of perceptual learning. Nature 387 (6631), Alvarez, G.A., and Cavanagh, P. (2005). Independent resources for attentional tracking in the left and right visual hemifields. Psychological Science 16 (8), Awh, E., and Pashler, H. (2000). Evidence for split attentional foci. Journal of Experimental Psychology: Human Perception and Performance 26 (2), Reardon, K., and Matthews, N. (2008). Bilateral superiority in discrimination and detection. Manuscript submitted for publication. Standard: BilateralStandard: UnilateralControl: BilateralControl: Unilateral Target/ Distracter Configurations Range-finding day to establish individual stimulus durations to avoid floor and ceiling effects Pre-test with participant-specific parameters 5 training days; 10 trained bilaterally, 10 unilaterally Post-test identical to pre-test Training ParadigmAdditional Experiments Comparison of performance on standard task with performance when target/ distracter positions inverted Varied duration of central letter: 67, 117, or 167 ms Comparison of distracter effects when aligned vertically or horizontally with targets * Abstract Linear Trends of Letter Duration Effects Letter, No Distracter F(1,19)=5.729, p=0.027, partial  2 =0.232 Letter, Distracter F(1,19)=9.345, p=0.006, partial  2 =0.330 Detection, No Distracter F(1,19)=4.219, p=0.054, n.s., partial  2 =0.182 Detection, Distracter F(1,19)=10.586, p=0.004, partial  2 =0.358 Overall, the results indicate that substantial learning occurred. It was predicted that learning would be specific to training condition, possibly because participants would become more adept at ignoring retinotopically specific distracter locations. This was not supported by the data; no significant specificity of learning was found for the variable of laterality. There was, however, evidence of location-specific improvement. Trained participants tested with inverted target/ distracter positions performed better with the standard than with the inverted configurations, irrelevant of the presence or absence of distracters. This superior ability in detecting targets in the standard locations suggests retinotopic learning in target positions, which would explain why learning was not specific to laterality condition; both laterality conditions involved training at all four standard locations. While this evidence exists for retinotopy, some of the results may be best explained by a concept of attentional resources. In particular, increasing the foveal task difficulty in the letter duration experiment was detrimental to peripheral performance, suggesting that increased demands in the center of the visual field reduced the resources available for the secondary task of detection. An attentional explanation is also consistent with the finding that the bilateral superiority effect only appears in the presence of distracters. That is, the distracters might increase the attentional demand of the task. There may have been a combination of retinotopic and attentional phenomena at work in this study. In general, the bilateral superiority effect does not appear to result from the orientation of target/ distracter alignment; the results of the displacement orientation control experiment instead suggest that the magnitude of laterality plays an important role. This perceptual learning study investigated whether participants trained on a visual detection task would demonstrate improvement specific to whether they were trained bilaterally (stimuli distributed between the left and right visual hemifields) or unilaterally (stimuli presented entirely within one hemifield). Substantial perceptual learning occurred overall, but this learning transferred between the two laterality conditions. There was evidence that participants made retinotopically specific improvements at trained target locations rather than learning to ignore specific distracter locations. Effects of distracters appear to result from increased demands placed on a more general cortical resource, evidence of which emerges in the form of sensory detriment induced by manipulating the difficulty of an associated foveal task.