Wonyeong Sohn

Learning to suppress task-irrelevant visual stimuli with attention

While the importance of attention in perceptual learning is widely recognized, the mechanisms through which it affects learning are poorly understood. Here we show that attentional mechanisms themselves are modified during learning. Attentional suppression of task-irrelevant stimuli becomes more efficient with practice. Attentional learning was found to be stimulus-specific and to persist for several weeks, suggesting that the plasticity of attentional mechanisms is an inherent component of visual perceptual learning.

Object-based cross-feature attentional modulation from color to motion.

Object-based theories of visual attention predict that attempting to direct attention to a particular attribute of a visual object will result in an automatic selection of the whole object, including all of its features. It has been assumed, but not critically tested, that the spreading of attention from one feature to another in this manner, i.e. cross-feature attentional (CFA) effects, takes place at object-level stages of processing as opposed to early, local stages. In the present study we disambiguated these options for color-to-motion CFA by contrasting attentions effect on bivectorial transparent versus bivectorial locally paired motion displays. We found that association between features at the global, but not at the local, stage of motion processing leads to cross-feature attentional effects. These findings provide strong psychophysical evidence that such effects are indeed object-based.

Motion aftereffects specific to surface depth order: beyond binocular disparity.

Despite evidence for concurrent processing of motion and stereopsis from psychophysics and neurophysiology, the detailed relationship between depth and motion processing is not yet clear. Using the contingent aftereffect paradigm, we investigated how the order of surfaces presented across depth influenced motion perception. After having observers adapt to two superimposed populations of dots moving in opposite directions at different binocular disparities, we assessed how much of the motion aftereffect (MAE) was specific to absolute disparity and how much was specific to the depth order of the surfaces. The test contained two planes of moving dots at several different pairs of disparities and asked observers to report the MAE direction at one of the planes (the target). In addition to the disparity-contingent MAE (Verstraten, Verlinde, Fredericksen, & van de Grind, 1994), we found MAEs dependent on surface order. When the target surface was in front of another surface, observers more often reported the MAE in the direction opposite to the front adapting surface than the back. This effect was observed despite differences in absolute and relative disparity between the adapted and test surfaces. The results suggest that some motion information is represented in terms of surface depth order.