Organizer: Marc Ernst& Irene Senna, Ulm University
Abstract: Would a person born blind who regained sight via some surgical intervention be able to learn to ‘see’? That is, would that individual be able to interpret the images that reach the retina and combine them with other senses in order to build a multisensory representation of the world, and to interact with the environment?
Surgically treating congenitally blind individuals (e.g., born with bilateral cataract) after extended periods of blindness provides a unique opportunity to study the development of visual skills, and the ability to combine vision with other senses.
For example, whether newly sighted individuals can learn to use their vision to recognize objects previously recognized only through touch, and to build multimodal representation of objects is still an open question. Behavioural and neural compensatory mechanisms in other sensory modalities are normally associated with blindness, but are such compensatory mechanisms maintained after sight restoration? Moreover, is the developmental path of such individuals similar to normal visual learning in early childhood and which are the factors that might limit perceptual learning? Deprivation from vision during the so-called critical periods might result in irreversible changes impairing the ability to interpret crucial aspects of visual and multisensory scenes. Are there critical periods for the development of the ability to integrate multisensory signals and to use vision for guiding action?
The proposed symposium aims to shed light on the development of visual and multisensory skills after sight restoration. In particular, the focus of the symposium will be on acquisition of visual function from multisensory information, and the use of these new perceptions for guiding actions.
S1.1 Learning to See Late in Childhood
Pawan Sinha Department of Brain and Cognitive Sciences, MIT
‘Project Prakash’ is an initiative launched over a decade ago with the goal of providing sight surgeries to blind children from medically underserved communities in the developing world. In pursuing this humanitarian mission, the project is helping address questions regarding brain plasticity and learning. Through a combination of behavioral and brain-imaging studies, the effort has provided a picture of the landscape of visual learning late in childhood and has illuminated some of the processes that might underlie aspects of such learning. I shall present an overview of some of our studies, which highlight the point that evidence of proficiencies as well as deficiencies in children’s performance after sight onset is potentially informative about the nature of developmental processes. Both of these kinds of results have pointed to theoretically interesting questions that we have attempted to address using computational techniques.
S1.2 How experience shapes brain specializations in the absence of vision
Amir Amedi Hebrew University of Jerusalem
I will discuss work aiming at unraveling the properties driving the sensory brain organization and at uncovering the extent to which specific unisensory experiences during critical periods are essential (or not essential) for the development of the natural sensory specializations. Our work focused on two fundamental discoveries: 1- Using the congenitally blind adult brain as a working model from a brain developing without any visual experience, we documented that essentially most if not all higher-order ‘visual’ cortices do maintain their anatomically consistent category-selectivity (e.g., for body shapes, letters, numbers or faces) even if the input is provided by an atypical sensory modality learned in adulthood, and that such task-specific sensory-independent specializations emerge after few hours of specific training (e.g. Abboud et al., 2015 Nat Comm; Amedi et al Trends Cog Sci 2017). Our work strongly encourages a paradigm shift in the conceptualization of our sensory brain by suggesting that visual experience during critical periods is not necessary to develop anatomically consistent specializations in higher-order ‘visual’ regions. We also propose the potential mechanisms underlying the emergence of sensory brain specializations independently of visual experience: a) pre-programmed sensory-independent task-specific computations that each specialized area/network processes (e.g., shape analysis for letter symbols independently of the sensory modality); and (b) partly innate network connectivity biases linking each specific cortical area to the rest of the brain (Heimler et al., 2015 Curr Opin Neurobiol; Hannagan et al., 2015 TICS; Amedi et al., 2017 TICS). Our emphasis on the task-selective and sensory independent brain organization also led to a paradigm shift in rehabilitation by suggesting that multisensory rather than unisensory training might be more effective in cases of sensory restoration (e.g. Reich et al Curr Opion in Neuorl; Heimler et al., 2015 Curr Opin Neurobiol; Amedi et al TICS 2017).
S1.3 Motion processing after sight restoration: No competition between visual recovery and auditory compensation
Davide Bottari*, R. Kekunnaya, M. Hense, N. F. Troje, S. Sourav, B. Röder IMT School for Advanced Studies Lucca
In the present study we tested whether functional adaptations following congenital blindness are maintained in humans after sight-restoration and whether they interfere with visual recovery. It has been shown that early permanently blind individuals outperform sighted controls in auditory motion processing and that auditory motion stimuli elicit activity in typical visual motion areas. Yet it is unknown what happens to these behavioral adaptations and cortical reorganizations when sight is restored. We employed a combined behavioral-electrophysiological approach in a group of sight-recovery individuals with a history of a transient phase of congenital blindness lasting for several months to several years. They, as well as two control groups, one with visual impairments, were tested in a visual and an auditory motion discrimination experiment. Task difficulty was manipulated by varying the visual motion coherence and the signal to noise ratio, respectively. The congenital cataract-reversal individuals showed lower performance in the visual global motion task than both control groups. At the same time, they outperformed both control groups in auditory motion processing suggesting that at least some compensatory behavioral adaptation due to the congenital blindness was maintained. Alpha oscillatory activity during the visual task was significantly lower in congenital cataract reversal individuals and they did not show ERPs modulated by visual motion coherence as observed in both control groups. In contrast, beta oscillatory activity in the auditory task, which varied as a function of SNR in all groups, was overall enhanced in congenital cataract reversal individuals. These results suggest that intramodal plasticity elicited by a transient phase of blindness was maintained and might mediate the prevailing auditory processing advantages in congenital cataract reversal individuals. By contrast, auditory and visual motion processing do not seem to compete for the same neural resources.
S1.4 A brief period of early visual deprivation alters cross-modal interactions
Batsheva Hadad University of Haifa
We examined whether a short and transient period of visual deprivation early in life is sufficient to induce lifelong changes in how the different sensory modalities interact and integrate. The first set of experiments examined visual dominance in a group of adults who had been treated for congenital bilateral cataracts during early infancy compared to a group of normally sighted controls. A version of the Colavita paradigm was used with a task requiring simple detection of visual and auditory targets, presented alone or in combination. The results showed that although the absence of early visual input is shown to increase sensitivity (reducing thresholds) for simple auditory inputs, it does not prevent the development of visual over auditory dominance. Another set of experiments examined the links between magnitude estimation across modalities in the two groups, measuring JNDs for a standard stimulus of 250 ms duration in one modality (e.g., Gaussian blobs in the visual domain), while embedded within stimuli of the other modality (e.g., pure tones). In each case, stimuli were presented within either a relatively narrow range of standard durations of 200 and 300 ms, or within a wider range of 100 and 400 ms. In the normally sighted controls, the range of magnitude affected discrimination thresholds, producing greater JNDs for wider ranges of stimulus magnitudes. Auditory context affected perceptual resolutions in vision, and visual context affected those in the auditory domain. In comparison to controls, cataract-reversal patients showed greater context effects of auditory stimuli on the perceptual resolutions in vision while reduced context effects of visual stimuli on the perceptual resolutions in audition. These results reveal that the absence of visual input early in life does not prevent the development of sensory dominance but modulates audiovisual interactions such that the effects of auditory input on vision are enhanced.
S1.5 Impairment of automatic “vision for action” functions in the newly sighted, following prolonged visual deprivation
Ayelet McKyton*, Ehud Zohary Hebrew University of Jerusalem
The ultimate goal of vision is to direct action. Some of our actions are triggered by automatic processes elicited by observing others’ actions: Infants can recognize the target of gaze of others, and direct their gaze to the same object within months from birth (termed “shared gaze”). Similarly, we are faster and better imitating actions when they are spatially congruent with others’ actions. Still, it is unclear if these automatic actions, elicited by viewing others, are innate or require visual experience to develop. We tackled this issue by studying a unique group of newly-sighted children that suffered from dense bilateral cataract from early infancy. After cataract removal surgery, their visual acuity typically improved allowing most of them to recognize hand actions or gaze direction. We then tested whether viewing a hand action (performed by others), would facilitate the response-compatible action and slow the incompatible one (automatic imitation effect). We also checked whether a pre-cue (showing a face with a specific gaze direction) would facilitate reaction to the gaze-compatible target (when compared to the gaze-incompatible location).The newly-sighted were less affected by task-irrelevant viewed-actions (hand action or gaze direction) than controls even two years after the operation. This strongly suggests that visual experience is necessary for the development of automatic imitation and shared gaze behaviour. At the very least, our results indicate that if these behaviours were based on innate mechanisms, they are clearly susceptible to long periods of visual deprivation.
S1.6 Multisensory perception for action in newly sighted individuals
Irene Senna, Sophia Pfister, Marc Ernst*
In our daily life we constantly and effortlessly integrate vision with other sensory signals to build knowledge of the world, and to generate and guide actions. However, would you be able to integrate multisensory signals and to plan visually guided actions if you were deprived of vision during early development? We tested Ethiopian children who were classified congenitally blind as they suffered from dense bilateral cataract during early post-natal development, and were surgically treaded years later (5-19 yo). In a series of perturbation experiments, we assessed these individuals’ ability to integrate visual information with other sensory signals, and to use visual feedback to guide actions. For instance, we asked participants to haptically explore objects while simultaneously looking at them through a magnifying lens (thus, inducing a discrepancy between senses). With such perturbation tasks, we aimed to investigate whether newly sighted individuals are able to integrate multisensory signals and make use of this newly acquired sense. In other tasks, we asked participants to wear prism goggles that shifted the apparent location of the target (i.e., inducing a systematic error between the apparent target’s position and the motor command needed to reach it). With this task we tested whether cataract reversal individuals are able to minimize the systematic errors by recalibrating the sensorimotor systems, as sighted individuals do. The results provide important insights into their sensorimotor learning skills, which are essential for using vision to guide actions. Preliminary results suggest that sight-recovered children weigh vision systematically less compared with typically developing-children, and are less able to recalibrate the sensorimotor system. This suggests that the newly sighted make use of the visual sense in the concert with the other senses, but also that they may require time to fully exploit its potentials.