Benedetta Heimler

Origins of task-specific sensory-independent organization in the visual and auditory brain: neuroscience evidence, open questions and clinical implications.

Evidence of task-specific sensory-independent (TSSI) plasticity from blind and deaf populations has led to a better understanding of brain organization. However, the principles determining the origins of this plasticity remain unclear. We review recent data suggesting that a combination of the connectivity bias and sensitivity to task-distinctive features might account for TSSI plasticity in the sensory cortices as a whole, from the higher-order occipital/temporal cortices to the primary sensory cortices. We discuss current theories and evidence, open questions and related predictions. Finally, given the rapid progress in visual and auditory restoration techniques, we address the crucial need to develop effective rehabilitation approaches for sensory recovery.

Response speed advantage for vision does not extend to touch in early deaf adults

Early deaf adults typically respond faster than hearing controls when performing a speeded simple detection on visual targets. Whether this response time advantage can generalise to another intact modality (touch) or it is instead specific to visual processing remained unexplored. We tested eight early deaf adults and twelve hearing controls in a simple detection task, with visual or tactile targets delivered on the arms and occupying the same locations in external space. Catch trials were included in the experimental paradigm. Results revealed a response time advantage in deaf adults compared to hearing controls, selectively for visual targets. This advantage did not extend to touch. The number of anticipation errors was negligible and comparable in both groups. The present findings strengthen the notion that response time advantage in deaf adults emerges as a consequence of changes specific to visual processing. They also exclude the involvement of sensory-unspecific cognitive mechanisms in this improvement (e.g. increased impulsivity in initiation of response, longer-lasting sustained attention or higher motivation to perform the task). Finally, they provide initial evidence that the intact sensory modalities can reorganise independently from each other following early auditory deprivation.

Task Selectivity as a Comprehensive Principle for Brain Organization

How do the anatomically consistent functional selectivities of the brain emerge? A new study by Bola and colleagues reveals task selectivity in auditory rhythm-selective areas in congenitally deaf adults perceiving visual rhythm sequences. Here, we contextualize this result with accumulating evidence from animal and human studies supporting sensory-independent task specializations as a comprehensive principle shaping brain (re)organization.

Stimulus- and goal-driven control of eye movements: Action videogame players are faster but not better

Action videogame players (AVGPs) have been shown to outperform nongamers (NVGPs) in covert visual attention tasks. These advantages have been attributed to improved top-down control in this population. The time course of visual selection, which permits researchers to highlight when top-down strategies start to control performance, has rarely been investigated in AVGPs. Here, we addressed specifically this issue through an oculomotor additional-singleton paradigm. Participants were instructed to make a saccadic eye movement to a unique orientation singleton. The target was presented among homogeneous nontargets and one additional orientation singleton that was more, equally, or less salient than the target. Saliency was manipulated in the color dimension. Our results showed similar patterns of performance for both AVGPs and NVGPs: Fast-initiated saccades were saliency-driven, whereas later-initiated saccades were more goal-driven. However, although AVGPs were faster than NVGPs, they were also less accurate. Importantly, a multinomial model applied to the data revealed comparable underlying saliency-driven and goal-driven functions for the two groups. Taken together, the observed differences in performance are compatible with the presence of a lower decision bound for releasing saccades in AVGPs than in NVGPs, in the context of comparable temporal interplay between the underlying attentional mechanisms. In sum, the present findings show that in both AVGPs and NVGPs, the implementation of top-down control in visual selection takes time to come about, and they argue against the idea of a general enhancement of top-down control in AVGPs.

Finding the balance between capture and control: Oculomotor selection in early deaf adults

Previous work investigating the consequence of bilateral deafness on attentional selection suggests that experience-dependent changes in this population may result in increased automatic processing of stimulus-driven visual information (e.g., saliency). However, adaptive behavior also requires observers to prioritize goal-driven information relevant to the task at hand. In order to investigate whether auditory deprivation alters the balance between these two components of attentional selection, we assessed the time-course of overt visual selection in deaf adults. Twenty early-deaf adults and twenty hearing controls performed an oculomotor additional singleton paradigm. Participants made a speeded eye-movement to a unique orientation target, embedded among homogenous non-targets and one additional unique orientation distractor that was more, equally or less salient than the target. Saliency was manipulated through color. For deaf participants proficiency in sign language was assessed. Overall, results showed that fast initiated saccades were saliency-driven, whereas later initiated saccades were goal-driven. However, deaf participants were overall slower than hearing controls at initiating saccades and also less captured by task-irrelevant salient distractors. The delayed oculomotor behavior of deaf adults was not explained by any of the linguistic measures acquired. Importantly, a multinomial model applied to the data revealed a comparable evolution over time of the underlying saliency- and goal-driven processes between the two groups, confirming the crucial role of saccadic latencies in determining the outcome of visual selection performance. The present findings indicate that prioritization of saliency-driven information is not an unavoidable phenomenon in deafness. Possible neural correlates of the documented behavioral effect are also discussed.

The oculomotor salience of flicker, apparent motion and continuous motion in saccade trajectories

The aim of the present study was to investigate the impact of dynamic distractors on the time-course of oculomotor selection using saccade trajectory deviations. Participants were instructed to make a speeded eye movement (pro-saccade) to a target presented above or below the fixation point while an irrelevant distractor was presented. Four types of distractors were varied within participants: (1) static, (2) flicker, (3) rotating apparent motion and (4) continuous motion. The eccentricity of the distractor was varied between participants. The results showed that saccadic trajectories curved towards distractors presented near the vertical midline; no reliable deviation was found for distractors presented further away from the vertical midline. Differences between the flickering and rotating distractor were found when distractor eccentricity was small and these specific effects developed over time such that there was a clear differentiation between saccadic deviation based on apparent motion for long-latency saccades, but not short-latency saccades. The present results suggest that the influence on performance of apparent motion stimuli is relatively delayed and acts in a more sustained manner compared to the influence of salient static, flickering and continuous moving stimuli.

Multisensory Interference in Early Deaf Adults

Multisensory interactions in deaf cognition are largely unexplored. Unisensory studies suggest that behavioral/neural changes may be more prominent for visual compared to tactile processing in early deaf adults. Here we test whether such an asymmetry results in increased saliency of vision over touch during visuo-tactile interactions. About 23 early deaf and 25 hearing adults performed two consecutive visuo-tactile spatial interference tasks. Participants responded either to the elevation of the tactile target while ignoring a concurrent visual distractor at central or peripheral locations (respond to touch/ignore vision), or they performed the opposite task (respond to vision/ignore touch). Multisensory spatial interference emerged in both tasks for both groups. Crucially, deaf participants showed increased interference compared to hearing adults when they attempted to respond to tactile targets and ignore visual distractors, with enhanced difficulties with ipsilateral visual distractors. Analyses on task-order revealed that in deaf adults, interference of visual distractors on tactile targets was much stronger when this task followed the task in which vision was behaviorally relevant (respond to vision/ignore touch). These novel results suggest that behavioral/neural changes related to early deafness determine enhanced visual dominance during visuo-tactile multisensory conflict.

The Implications of Brain Plasticity and Task Selectivity for Visual Rehabilitation of Blind and Visually Impaired Individuals

The human brain is a formidably complex and adaptable organ capable of rewiring itself or adjusting existing connections in order to learn and to maximize its survival edge. Studies using sensory substitution devices have had a big impact on the uncovering of the mechanisms subtending brain organization. Sensory substitution devices are capable of conveying information typically received through a specific sensory modality (e.g., vision) and transferring it to the user via a different sense (e.g., audition or touch). Experimental research exploring the perceptual learning of sensory substitution devices has revealed the ability of users to recognize movement and shapes, to navigate routes, to detect and avoid obstacles, and to perceive colors or depth via touch or sound, even in cases of full and congenital blindness. Using a combination of functional and anatomical neuroimaging techniques, the comparisons of performances between congenitally blind people and sighted people using sensory substitution devices in perceptual and sensory-motor tasks as well as in several recognition tasks uncovered the striking ability of the brain to rewire itself during perceptual learning and to learn to interpret novel sensory information even during adulthood. This review discusses the impact of invasive and noninvasive forms of artificial vision on brain organization with a special emphasis on sensory substitution devices and also discusses the implications of these findings for the visual rehabilitation of congenitally and late blind and partially sighted individuals while applying insights from neuroimaging and psychophysics.

Multisensory flexibility within a perceptual system reorganized by crossmodal plasticity

The widespread intuition that sensory deprivation should enhance processing in the intact modalities has been primarily tested in unisensory contexts. This approach has the limit of not probing for potential changes in the interaction between intact modalities, ultimately not allowing to conclude whether documented unisensory advantages always dominate behavior. Here we examined whether deafness modifies the interactions between vision and touch, and to what extent enhanced processing of peripheral visual events — repeatedly documented in unisensory studies of deafness — dominates behavior also in a multisensory context in which vision is entirely task-irrelevant. Nine hearing and seven early-deaf adults performed two visuo-tactile tasks. In one task, participants responded to the elevation of a tactile stimulus while ignoring a concurrent visual stimulus (central or peripheral). The distractor was spatially congruent or incongruent with the target. The other task was reversed (i.e., respond to vision, ignore touch). Visuo-tactile interference emerged for all participants, revealing similar multisensory processing in the two groups. However, when vision was task relevant, deaf people were distracted by touch less than hearing controls when visual targets were peripheral. This reveals the expected enhanced processing for peripheral visual stimuli in deafness. Strikingly, when vision was task irrelevant (i.e., respond to touch) comparable visuo-tactile interference emerged in the two groups for both visual distractor eccentricities. These findings show that enhanced processing of peripheral visual information in deafness can be modulated as a function of task-demands, revealing a remarkable multisensory flexibility within a perceptual system reorganized by crossmodal plasticity.

The impact of saliency on overt visual selection in early-deaf adults

Following bilateral deafness, vision reorganizes to overcome the lack of audition. Results from covert attention studies show enhanced reactivity and rapid attention orienting to abrupt visual stimuli in deaf people, suggesting that crossmodal changes may prioritize saliency-driven attention capture in this population. However, deaf individuals also need to maintain goal-directed behaviors. We investigated the time-course of overt visual selection in deaf adults, to assess when in time deaf individuals implement efficient top-down control over saliency-driven search. Eighteen early-deaf adults and sixteen hearing controls performed an oculomotor additional singleton paradigm. For deaf participants language abilities in oral and sign languages were assessed. Participants made a speeded saccadic eye movement to a unique orientation singleton. The target was presented among homogenous non-targets and one additional orientation singleton that was more, equally or less salient than the target. Results showed a similar pattern of performance in the two groups: fast initiated saccades were saliency-driven whereas later initiated saccades were more goal-driven. However, deaf were overall slower than hearing participants at initiating saccades. This delay in saccadic latencies was driven by a sub-group of deaf adults, who were able to bypass saliency capture by withholding their saccades until target selection was efficiently achieved. No correlation with linguistic abilities emerged, showing no role of sign language acquisition in this behavior. Taken together, the present findings reveal that overt visual reorganization in deaf adults does not drastically alter the interplay between bottom-up and top-down strategies. If anything, it prioritizes the implementation of efficient goal-directed behaviors.