Adaptation to leftward-shifting prisms enhances local processing in healthy individuals

Abstract

In healthy individuals, adaptation to left-shifting prisms has been shown to simulate the symptoms of hemispatial neglect, including a reduction in global processing that approximates the local bias observed in neglect patients. The current study tested whether leftward prism adaptation can more specifically enhance local processing abilities. In three experiments, the impact of local and global processing was assessed through tasks that measure susceptibility to illusions that are known to be driven by local or global contextual effects. Susceptibility to the rod-and-frame illusion – an illusion disproportionately driven by both local and global effects depending on frame size – was measured before and after adaptation to left- and right-shifting prisms. A significant increase in rod-and-frame susceptibility was found for the left-shifting prism group, suggesting that adaptation caused an increase in local processing effects. The results of a second experiment confirmed that leftward prism adaptation enhances local processing, as assessed with susceptibility to the simultaneous-tilt illusion. A final experiment employed a more specific measure of the global effect typically associated with the rod-andframe illusion, and found that although the global effect was somewhat diminished after leftward prism adaptation, the trend failed to reach significance (p = .078). Rightward prism adaptation had no significant effects on performance in any of the experiments. Combined, these findings indicate that leftward prism adaptation in healthy individuals can simulate the local processing bias of neglect patients primarily through an increased sensitivity to local visual cues, and confirm that prism adaptation not only modulates lateral shifts of attention, but also prompts shifts from one level of processing to another.

Modulation of visual attention by prismatic adaptation

“…Focusing attention on global aspects activates the right lingual gyrus, focusing it on local aspects the left inferior occipital cortex, whereas sustained attention to global or to local aspects involves the temporo-parietal cortex bilaterally, as well as additional parts of the right fronto-parietal cortex including its dorsal parts. Normal subjects are faster identifying global than local information and have difficulties ignoring global information when focusing on local level; rightward PA did not change this bias (Bultitude and Woods, 2010;Reed and Dassonville, 2014). Right hemispheric damage, and neglect in particular, have been found to be associated with hyperattention to local details and with a deficit in perceiving the global structure of stimuli (Delis et al, 1986;Marshall and Halligan, 1995;Robertson et al, 1988).…”

Beyond the Sensorimotor Plasticity: Cognitive Expansion of Prism Adaptation in Healthy Individuals

“…After adaptation to a leftward optical deviation, there was a significant reduction in global interference similar to the processing bias demonstrated in patients with right temporo-parietal junction lesions ( Bultitude et al, 2009 ). Reed and Dassonville (2014) demonstrated that adaptation to a leftward optical deviation increased the susceptibility to a subset of visual illusions known to be driven by local contextual processing. However, adaptation failed to influence performance in the composite face task that is supposed to evaluate the automatic global-level processing of faces ( Bultitude et al, 2013a ).…”

“…Otherwise, the hand used during prism exposure may have a potential influence on the hemispheric imbalance following adaptation. Except two studies ( Michel et al, 2008 ; Reed and Dassonville, 2014 ) using both hands for visuo-manual pointings during prism exposure, the right dominant hand (involving the left hemisphere) is always used.…”

Unchanged EEG correlates of covert visual spatial attention after prism adaptation in healthy subjects

“…While the first two parameters are known, the effect size has to be estimated based on the literature. We computed the Cohen's d effect size of prism adaptation on behavioural outcome measures in healthy subjects from previous studies that reported the mean and standard deviation or standard error of their detected difference (Bultitude, Van der Stigchel, & Nijboer, 2013;Colent, Pisella, Bernieri, Rode, & Rossetti, 2000;Michel et al, 2003;Reed & Dassonville, 2014). These effect sizes ranged from 0.18 to 1.4, with an average of 0.75 standard deviations.…”