Browsing by Author "Sowden, P. T."

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Open Access
Chromatic perceptual learning
(John Benjamins Publishing Company, 2011) Sowden, P. T.; Davies, I. R. L.; Notman, L. A.; Alexander, I.; Özgen, Emre; Biggam, C. P.; Hough, C. A.; Kay, C. J.; Simmons, D. R.
Perceptual learning has been shown on a wide variety of achromatic visual tasks. However, very little work has explored the possibility of improvements on chromatically based tasks. Here, we used a transfer of learning paradigm to assess the specificity of improvements at discriminating the orientation of a chromatically defined edge presented in luminance noise. Chromatic thresholds were estimated for two different hues and retinal locations, before and after a ten day training period. During training observers discriminated the orientation of a chromatic edge at just one location and hue. Whilst performance improved following training, these improvements failed to transfer across either retinal location or hue. Our findings suggest that improvements in chromatically-mediated discrimination may involve plasticity at early, retinotopically mapped, stages of visual analysis. Further, they suggest that categorical perception of colour might in part arise from chromatic perceptual learning at colour category boundaries.
Open Access
Retinotopic sensitisation to spatial scale: evidence for flexible spatial frequency processing in scene perception
(Elsevier Ltd., 2006) Ozgen, E.; Payne, H. E.; Sowden, P. T.; Schyns, P. G.
Observers can use spatial scale information flexibly depending on categorisation task and on their prior sensitisation. Here, we explore whether attentional modulation of spatial frequency processing at early stages of visual analysis may be responsible. In three experiments, we find that observers' perception of spatial frequency (SF) band-limited scene stimuli is determined by the SF content of images previously experienced at that location during a sensitisation phase. We conclude that these findings are consistent with the involvement of relatively early, retinotopically mapped, stages of visual analysis, supporting the attentional modulation of spatial frequency channels account of sensitisation effects.
Open Access
Top-down attentional modulation of spatial frequency processing in scene perception
(Routledge, 2005) Özgen E.; Sowden, P. T.; Schyns, P. G.; Daoutis, C.
Recent evidence suggests that spatial frequency (SF) processing of simple and complex visual patterns is flexible. The use of spatial scale in scene perception seems to be influenced by people's expectations. However as yet there is no direct evidence for top-down attentional effects on flexible scale use in scene perception. In two experiments we provide such evidence. We presented participants with low-and high-pass SF filtered scenes and cued their attention to the relevant scale. In Experiment 1 we subsequently presented them with hybrid scenes (both low- and high-pass scenes present). We observed that participants reported detecting the cued component of hybrids. To explore if this might be due to decision biases, in Experiment 2, we replaced hybrids with images containing meaningful scenes at uncued SFs and noise at the cued SFs (invalid cueing). We found that participants performed poorly on invalid cueing trials. These findings are consistent with top-down attentional modulation of early spatial frequency processing in scene perception.