The Multifaceted effects of blindness and how sight might be restored

Symposium: Friday, May 17, 2024, 5:00 – 7:00 pm, Talk Room 1

Schedule of Events | Search Abstracts | Symposia | Talk Sessions | Poster Sessions

Organizer: Ella Striem-Amit¹; ¹Georgetown University
Presenters: Lara Coelho, Santani Teng, Woon Ju Park, Elizabeth J. Saccone, Ella Striem-Amit, Michael Beyeler

Congenital blindness illustrates the developmental roots of visual cortex functions. Here, a group of early-career researchers will present various perspectives on the multifaceted effects of blindness on the brain and behavior. To start off the symposium, Coelho will describe the effect of sight loss on multisensory properties, and the reliance on vision to develop an intact multisensory body representation. This presentation will highlight the dependence across modalities, revealing rich interactions between vision and body representations. Discussing a unique manifestation of compensation in blindness, Teng will discuss how echolocation functions in naturalistic settings and its properties of active sensing. Continuing the theme of integration across senses and diving into visual cortical reorganization, Park will argue for partial dependence and partial independence on vision for the development of motion processing in hMT+. Saccone will show evidence for a functional takeover of language over typically face-selective FFA in blindness, showing plasticity beyond sensory representations. Together, these two talks will highlight different views of brain plasticity in blindness. Adding to our discussion of the multifaceted nature of plasticity, Striem-Amit will discuss whether plasticity in the visual cortex is consistent across different blind individuals, showing evidence for divergent visual plasticity and stability over time in adulthood. The last speaker will discuss the challenges and potential for sight restoration using visual prostheses. Beyeler will discuss how some of the challenges of sight restoration can be addressed through perceptual learning of implant inputs. This talk highlights how understanding plasticity in the visual system and across the brain has direct applications for successfully restoring sight. Together, the symposium will bring different theoretical perspectives to illustrate the effects of blindness, revealing the extent and diversity of neural plasticity, and clarify the state-of-the-art capacities for sight restoration.

Talk 1

Implications of visual impairment on body representation

Lara Coelho¹, Monica Gori; ¹Unit for visually impaired people, Italian Institute of Technology, Genova, Italy

In humans, vision is the most accurate sensory modality for constructing our representation of space. It has been shown that visual impairment negatively influences daily living and quality of life. For example, spatial and locomotor skills are reduced in this population. One possibility is that these deficiencies arise from a distorted representation of the body. Body representation is fundamental for motor control, because we rely on our bodies as a metric guide for our actions. While body representation is a by-product of multisensory integration, it has been proposed that vision is necessary to construct an accurate representation of the body. In the MySpace project, we are investigating the role of visual experience on haptic body representations in sighted and visually impaired (VI) participants. To this end, we employ a variety of techniques to investigate two key aspects of body representation 1) size perception, and 2)the plasticity of the proprioceptive system. These techniques include landmark localization, psychophysics, and the rubber hand illusion. Our results in sighted participants show distortions in haptic but not visual body representation. In the VI participants there are distortions when estimating forearm, hand, and foot size in several different haptic tasks. Moreover, VI children fail to update their perceived body location in the rubber hand illusion task. Collectively, our findings support the hypothesis that vision is necessary to reduce distortions in haptic body representations. Moreover, we propose, that VI children may develop with impaired representations of their own bodies. We discuss possible opportunities for reducing this impairment.

Talk 2

Acoustic glimpses: The accumulation of perceptual information in blind echolocators

Santani Teng¹; ¹Smith-Kettlewell Eye Research Institute

Blindness imposes constraints on the acquisition of sensory information from the environment. To mitigate those constraints, some blind people employ active echolocation, a technique in which self-generated sounds, like tongue “clicks,” produce informative reflections. Echolocating observers integrate over multiple clicks, or samples, to make perceptual decisions that guide behavior. What information is gained in the echoacoustic signal from each click? Here, I will draw from similar work in eye movements and ongoing studies in our lab to outline our approaches to this question. In a psychoacoustic and EEG experiment, blind expert echolocators and sighted control participants localized a virtual reflecting object after hearing simulated clicks and echoes. Left-right lateralization improved on trials with more click repetitions, suggesting a systematic precision benefit to multiple samples even when each sample delivered no new sensory information. In a related behavioral study, participants sat in a chair but otherwise moved freely while echoacoustically detecting, then orienting toward a reflecting target located at a random heading in the frontal hemifield. Clicking behavior and target size (therefore sonar strength) strongly influenced the rate and precision of orientation convergence toward the target, indicating a dynamic interaction between motor-driven head movements, click production, and the resulting echoacoustic feedback to the observer. Taken together, modeling these interactions in blind expert practitioners suggests similar properties, and potential shared mechanisms, between active sensing behavior in visual and echoacoustic domains.

Talk 3

Constraints of cross-modal plasticity within hMT+ following early blindness

Woon Ju Park¹, Kelly Chang, Ione Fine; ¹Department of Psychology, University of Washington

Cross-modal plasticity following early blindness has been widely documented across numerous visual areas, highlighting our brain’s remarkable adaptability to changes in sensory environment. In many of these areas, functional homologies have been observed between the original and reorganized responses. However, the mechanisms driving these homologies remain largely unknown. Here, we will present findings that aim to answer this question within the area hMT+, which responds to visual motion in sighted individuals and to auditory motion in early blind individuals. Our goal was to examine how the known functional and anatomical properties of this area influence the development of cross-modal responses in early blind individuals. Using a multimodal approach that encompasses psychophysics, computational modeling, and functional and quantitative MRI, we simultaneously characterized perceptual, functional, and anatomical selectivity to auditory motion within early blind and sighted individuals. We find that some anatomical and functional properties of hMT+ are inherited, while others are altered in those who become blind early in life.

Talk 4

Visual experience is necessary for dissociating face- and language-processing in the ventral visual stream

Elizabeth J. Saccone¹, Akshi¹, Judy S. Kim², Mengyu Tian³, Marina Bedny¹; ¹Department of Psychological and Brain Sciences, Johns Hopkins University, Baltimore, MD, USA, ²Center for Human Values, Princeton University, Princeton, NJ, USA, ³Center for Educational Science and Technology, Beijing Normal University at Zhuhai, China

The contributions of innate predispositions versus experience to face-selectivity in vOTC is hotly debated. Recent studies with people born blind suggest face specialization emerges regardless of experience. In blindness the FFA is said to process face shape, accessed through touch or sound, or maintain its behavioral role in person recognition by specializing for human voices. We hypothesized instead that in blind people the anatomical location of the FFA responds to language. While undergoing fMRI, congenitally blind English speakers (N=12) listened to spoken language (English), foreign speech (Russian, Korean, Mandarin), non-verbal vocalizations (e.g., laughter) and control non-human scene sounds (e.g., forest sounds) during a 1-back repetition task. Participants also performed a ‘face localizer’ task by touching 3D printed models of faces and control scenes and a language localizer (spoken words > backwards speech, Braille > tactile shapes). We identified individual-subject ROIs inside a FFA mask generated from sighted data. In people born blind, the anatomical location of the FFA showed a clear preference for language over all other sounds, whether human or not. Responses to spoken language were higher than to foreign speech or non-verbal vocalizations, which were not different from scene sounds. This pattern was observed even in parts of vOTC that responded more to touching faces. Specialization for faces in vOTC is influenced by experience. In the absence of vision, lateral vOTC becomes implicated in language. We speculate that shared circuits that evolved for communication specialize for either face recognition or language depending on experience.

Talk 5

Individual differences of brain plasticity in early visual deprivation

Ella Striem-Amit¹; ¹Department of Neuroscience, Georgetown University Medical Center, Washington, DC 20057, USA

Early-onset blindness leads to reorganization in visual cortex connectivity and function. However, this has mostly been studied at the group level, largely ignoring differences in brain reorganization across early blind individuals. To test whether plasticity manifests differently in different blind individuals, we studied resting-state functional connectivity (RSFC) from the primary visual cortex in a large cohort of blind individuals. We find increased individual differences in connectivity patterns, corresponding to areas that show reorganization in blindness. Further, using a longitudinal approach in repeatedly sampled blind individuals, we showed that such individual patterns of organization and plasticity are stable over time, to the degree of decoding individual participant identity over 2 years. Together, these findings suggest that visual cortex reorganization is not ubiquitous, highlighting the potential diversity in brain plasticity and the importance of harnessing individual differences for fitting rehabilitation approaches for vision loss.

Talk 6

Learning to see again: The role of perceptual learning and user engagement in sight restoration

Michael Beyeler¹; ¹University of California, Santa Barbara

Retinal and cortical implants show potential in restoring a rudimentary form of vision to people living with profound blindness, but the visual sensations (“phosphenes”) produced by current devices often seem unnatural or distorted. Consequently, the ability of implant users to learn to make use of this artificial vision plays a critical role in whether some functional vision is successfully regained. In this talk, I will discuss recent work detailing the potential and limitations of perceptual learning in helping implant users learn to see again. Although the abilities of visual implant users tend to improve with training, there is little evidence that this is due to distortions becoming less perceptually apparent, but instead may be due to better interpretation of distorted input. Unlike those with natural vision, implant recipients must accommodate various visual anomalies, such as inconsistent spatial distortions and phosphene fading. Furthermore, perceptual measures such as grating acuity and motion discrimination, which are often used with the intention of objectively assessing visual function, may be modulated via gamification, highlighting the importance of user engagement in basic psychophysical tasks. Gamification may be particularly effective at engaging reward systems in the brain, potentially fostering greater plasticity through more varied stimuli and active attentional engagement. However, the effectiveness of such gamified approaches varies, suggesting a need for personalized strategies in visual rehabilitation.