Biology subjects

Silva, A. E.

Publications and source records attributed to Silva, A. E..

6 recordsLinked to original sources

bioRxiv2023

Improving peripheral reading with non-invasive transcranial electrical stimulation of early visual areas

We investigated the ability of two non-invasive transcranial electrical stimulation (tES) protocols targeting early visual areas to improve peripheral visual word recognition in separate within-subject, double-blind, sham-controlled experiments with normal observers. English sentences were presented 10 degrees below fixation using a rapid serial visual presentation (RSVP). Transcranial random noise stimulation (tRNS) applied bilaterally on either size of the occipital pole (Oz) elicited a significant performance benefit, but transcranial direct current stimulation (tDCS) applied to Oz did not. These results highlight important factors that may influence the effectiveness of non-invasive brain stimulation methods for enhancing peripheral processing of text, such as stimulation type. While more work is necessary to better understand the relationship between tES and peripheral reading, the present results contribute to the growing body of work implicating tES as a potential tool for enhancing peripheral visual processing.

neuroscience↗

bioRxiv2023

Visual cortex anodal tDCS does not alter reading performance for Chinese presented character-by-character to normal peripheral vision

Visual cortex transcranial direct current stimulation (tDCS) reduces crowding in normal peripheral vision and may improve reading of English words in patients with macular degeneration. Given the different visual requirements of reading English words and Chinese characters, the effect of tDCS on peripheral reading performance in English might be different from Chinese. This study recruited seventeen participants (59 to 73 years of age) with normal vision and tested the hypothesis that anodal tDCS would improve reading of Chinese characters presented at 10{degrees} eccentricity compared with sham stimulation. Chinese sentences of different print sizes and exposure durations were presented one character at a time 10{degrees} below or to the left of fixation, and the individual critical print size (CPS) - the smallest print size eliciting the maximum reading speed (MRS) was determined. Reading accuracies for characters presented 0.2 logMAR smaller than the CPS were measured before, during, 5 mins, and 30 mins after receiving active or sham anodal visual cortex tDCS. Participants completed both the active and sham sessions in a random order following a double-blind, within-subject design. No effect of active anodal-tDCS on reading accuracy was observed, implying that a single session of tDCS did not improve Chinese character reading in normal peripheral vision. This may suggest that tDCS does not significantly reduce the crowding elicited within a single Chinese character. However, the effect of tDCS on between-character crowding is yet to be determined.

neuroscience↗

bioRxiv2020

Precise oculocentric mapping of TMS-evoked phosphenes

Transcranial Magnetic Stimulation (TMS) - evoked phosphenes are oculocentric; their perceived location depends upon eye position. We investigated the accuracy and precision of TMS-evoked phosphene oculocentric mapping and demonstrate that perceived phosphene locations map veridically to eye position, although there are considerable individual differences in the reliability of this mapping. Our results emphasize the need to carefully control eye movements when carrying out phosphene localization studies and suggest that individual differences in the reliability of the reported position of individual phosphenes must be considered.

neuroscience↗

bioRxiv2020

Motion opponency examined throughout visual cortex with multivariate pattern analysis of fMRI data

This study explores how the human brain solves the challenge of flicker noise in motion processing. Despite providing no useful directional motion information, flicker is common in the visual environment and exhibits omnidirectional motion energy which is processed by low-level motion detectors. Models of motion processing propose a mechanism called motion opponency that reduces the processing of flicker noise. Motion opponency involves the pooling of local motion signals to calculate an overall motion direction. A neural correlate of motion opponency has been observed in human area MT+/V5 using fMRI, whereby stimuli with perfectly balanced motion energy constructed from dots moving in counter-phase elicit a weaker BOLD response than non-balanced (in-phase) motion stimuli. Building on this previous work, we used multivariate pattern analysis to examine whether the patterns of brain activation elicited by motion opponent stimuli resemble the activation elicited by flicker noise across the human visual cortex. Robust multivariate signatures of opponency were observed in V5 and in V3A. Our results support the notion that V5 is centrally involved in motion opponency and in the reduction of flicker noise during visual processing. Furthermore, these results demonstrate the utility of powerful multivariate analysis methods in revealing the role of additional visual areas, such as V3A, in opponency and in motion processing more generally. HighlightsO_LIOpponency is demonstrated in multivariate and univariate analysis of V5 data. C_LIO_LIMultivariate fMRI also implicates V3A in motion opponency. C_LIO_LIMultivariate analyses are useful for examining opponency throughout visual cortex. C_LI

neuroscience↗

bioRxiv2019

Multi-session visual cortex transcranial random noise stimulation in adults with amblyopia

PurposeWe tested the hypothesis that five daily sessions of visual cortex transcranial random noise stimulation would improve contrast sensitivity, crowded and uncrowded visual acuity in adults with amblyopia. MethodsNineteen adults with amblyopia (44.2 {+/-} 14.9yrs, 10 female) were randomly allocated to active or sham tRNS of the visual cortex (active, n = 9; sham, n = 10). tRNS was delivered for 25 minutes across five consecutive days. Monocular contrast sensitivity, uncrowded and crowded visual acuity were measured before, during, 5 minutes and 30 minutes post stimulation on each day. ResultsActive tRNS significantly improved contrast sensitivity and uncrowded visual acuity for both amblyopic and fellow eyes whereas sham stimulation had no effect. An analysis of the day by day effects revealed large within session improvements on day 1 for the active group that waned across subsequent days. No long-lasting (multi-day) improvements were observed for contrast sensitivity, however a long-lasting improvement in amblyopic eye uncrowded visual acuity was observed for the active group. This improvement remained at 28 day follow up. However, between-group differences in baseline uncrowded visual acuity complicate the interpretation of this effect. No effect of tRNS was observed for amblyopic eye crowded visual acuity. ConclusionsIn agreement with previous non-invasive brain stimulation studies using different techniques, tRNS induced short-term contrast sensitivity improvements in adult amblyopic eyes, however, multiple sessions of tRNS did not lead to enhanced or long-lasting effects for the majority of outcome measures.

neuroscience↗

bioRxiv2019

Continuous theta burst TMS of area MT+ impairs attentive motiontracking.

Attentive motion tracking deficits, measured using multiple object tracking (MOT) tasks, have been identified in a number of visual and neurodevelopmental disorders such as amblyopia and autism. These deficits are often attributed to the abnormal development of high-level attentional networks. However, neuroimaging evidence from amblyopia suggests that reduced MOT performance can be explained by impaired function in motion sensitive area MT+ alone. To test the hypothesis that MT+ plays an important role in MOT, we assessed whether modulation of MT+ activity using continuous theta burst stimulation (cTBS) influenced MOT performance in participants with normal vision. An additional experiment involving numerosity judgements of MOT stimulus elements was conducted to control for non-specific effects of MT+ cTBS on psychophysical task performance. The MOT stimulus consisted of 4 target and 4 distractor dots and was presented at 10{degrees} eccentricity in the right or left hemifield. Functional MRI-guided cTBS was applied to left MT+. Participants (n = 13, age:27 {+/-} 3) attended separate active and sham cTBS sessions where the MOT task was completed before, 5 mins post and 30 mins post cTBS. Active cTBS significantly impaired MOT task accuracy relative to baseline for the right (stimulated) hemifield 5 mins (10 {+/-} 2% reduction; t12 = 1.95, p = 0.03) and 30 mins (14 {+/-} 3% reduction; t12 = 2.96, p = 0.01) post stimulation. No impairment occurred within the left (control) hemifield after active cTBS or for either hemifield after sham cTBS. Numerosity task performance was unaffected by cTBS. These results highlight the importance of lower-level motion processing for MOT and suggest that abnormal function of MT+ alone is sufficient to cause a deficit in MOT task performance.

neuroscience↗