The effect of blur on cortical responses to global form and motion

Abstract

Global form and motion sensitivity undergo long development in childhood with motion sensitivity rather than form being impaired in a number of childhood disorders and both impaired in adult clinical populations. This suggests extended development and vulnerability of extrastriate cortical areas associated with global processing. However, in some developmental and clinical populations, it remains unclear to what extent impairments might reflect deficits at earlier stages of visual processing, such as reduced visual acuity and contrast sensitivity. To address this, we investigated the impact of degraded spatial vision on cortical global form and motion processing in healthy adults. Loss of high spatial frequencies was simulated using a diffuser to blur the stimuli. Participants completed behavioral and EEG tests of global form and motion perception under three levels of blur. For the behavioral tests, participants' form and motion coherence thresholds were measured using a two-alternative, forced-choice procedure. Steady-state visual evoked potentials were used to measure cortical responses to changes in the coherence of global form and motion stimuli. Both global form and global motion perception were impaired with increasing blur as measured by elevated behavioral thresholds and reduced cortical responses. However, form thresholds showed greater impairment in both behavioral and EEG measures than motion thresholds at the highest levels of blur. The results suggest that high spatial frequencies play an important role in the perception of both global form and motion but are especially significant for global form. Overall, the results reveal complex interactions between low-level factors and global visual processing, highlighting the importance of taking these factors into account when investigating extrastriate function in low vision populations.

Concurrent Investigation of Global Motion and Form Processing in Amblyopia: An Equivalent Noise Approach

“…This would suggest that the under sampling theory posited for other visual deficits in amblyopia 36,49 could be applicable to global motion and form processing as well. These deficits do not seem to be dependent on the visibility of stimuli as has been reported before for normal participants, 50 as the fellow eyes of strabismic amblyopes which had similar visual acuity to the normal eyes (independent t-test, t (20) ¼ 1.25, P > 0.05) also showed raised thresholds for both motion and form domains.…”

Cortical processing of global form, motion and biological motion under low light levels

“…However, the effects on global form, motion and biological motion perception were not uniform, suggesting that spatial limitations of scotopic vision are insufficient in explaining midand higher-level visual performance under low light. Comparing the results to data previously collected photopically but with stimuli which were blurred in order to reduce the available spatial information, (Burton et al, 2015), scotopic form perception was less impaired than by blur leading to similar overall reductions in spatial vision. This suggests that the level of sensitivity in low light is greater than expected given the spatial impairments.…”

“…To test the extent to which reductions in global form and motion thresholds under low light could be explained by reductions in contrast sensitivity and acuity alone, results were compared to data collected previously in 20 typically sighted participants with simulated low vision (Burton et al, 2015). These participants completed the same coherent form and motion tests used here, viewed through a diffuser acting as a low pass filter at different separations from the screen which introduced different levels of blur.…”

“…We have investigated elsewhere (Burton et al, 2015) the effects of reduced acuity and contrast sensitivity on global form and motion processing. Scotopic vision also has relatively sluggish temporal properties, at least in central areas of the visual field, which may have an impact on motion processing (Conner, 1982;Takeuchi & De Valois, 2000).…”

Motion perception as a model for perceptual aging

“…Some findings indicate that acuity limits performance in motion tasks that require the detection of small spatial displacements, e.g., in apparent motion tasks (Roudaia, Bennett, Sekuler, & Pilz, 2010). Congruently, it has been shown that visual blur, i.e., degraded high spatial frequency information, impairs motion discrimination (Burton et al, 2015). However, the detrimental effect seems only moderate in comparison with the massive threshold increase observed for form perception.…”