Early Blind Individuals Research Articles

Assessment of spatial reasoning in blind individuals using a haptic version of the Kohs Block Design Test

• Early blind individuals show difficulties in manipulating haptic spatial configurations. • Late blind and sighted individuals report efficient spatial reasoning capabilities. • Performance in spatial reasoning task is not related to duration of blindness. • Adapted neuropsychological tests are efficient tools to assess the cognitive functioning of blind people. Past research investigating the spatial abilities of visually impaired people, provided conflicting results. There is thus an urgent need to develop standardized tests for the evaluation of spatial cognition when vision is absent or disrupted. To this aim, we developed a haptic version of the Kohs Block Design Test and investigated the spatial non-verbal reasoning of early blind, late blind and sighted individuals. Participants reproduced 3D printed haptic configurations by assembling blocks with different textures, within a time limit. Results showed that early blind individuals reproduced fewer haptic designs than the other two groups correctly. Instead, the assembling time of the correct responses was similar among all groups. Moreover, blindness duration (in years) did not seem to affect the correctness of the performance: no significant correlation between the two variables was observed for early and late blind participants. Since only early blind individuals display difficulties in mentally representing the haptic configurations and manipulating multiple spatial information, we conclude that early visual deprivation may affect spatial reasoning capabilities. The present study adds new insights on the role of visual experience in the development of spatial skills and represents a first step in the adaptation of standardized tests for the assessment of spatial cognitive abilities in visually impaired people.

Years of Blindness Lead to "Visualize" Space Through Time.

Spatial representation has been widely studied in early blindness, whereas research about late blindness is still limited. We recently demonstrated that the early (50–90 ms) event-related potential (ERP) response observed in sighted people during a spatial bisection task, is altered in early blind people and is influenced by the amount of time spent without vision in late blind individuals. Specifically, in late blind people a shorter period of blindness is associated with strong contralateral activation in occipital cortex and good performance during the spatial task–similar to that of sighted people. In contrast, non-lateralized occipital activation and lower performance characterize late blind individuals who have experienced a longer period of blindness–similar to that of early blind people. However, the same early occipital response activated in sighted individuals by spatial cues has been found to be activated by temporal cues in early blind individuals. Here, we investigate whether a similar temporal attraction can explain the neural and behavioral changes observed after many years of blindness in late blind people. An EEG recording was taken during a spatial bisection task where coherent and conflicting spatio-temporal information was presented. In participants with long blindness duration, the early recruitment of both visual and auditory areas is sensitive to temporal instead of spatial coordinates. These findings highlight some limits of neuroplasticity. Perceptual advantages from cross-sensory calibration during development seem to be subsequently lost following years of visual deprivation. This result has important implications for clinical outcomes following late blindness, highlighting the importance of timing in intervention and rehabilitation programs that activate compensatory strategies soon after sensory loss.

Late- but not early-onset blindness impairs the development of audio-haptic multisensory integration.

Integrating different senses to reduce sensory uncertainty and increase perceptual precision can have an important compensatory function for individuals with visual impairment and blindness. However, how visual impairment and blindness impact the development of optimal multisensory integration in the remaining senses is currently unknown. Here we first examined how audio-haptic integration develops and changes across the life span in 92 sighted (blindfolded) individuals between 7 and 70years of age. We used a child-friendly task in which participants had to discriminate different object sizes by touching them and/or listening to them. We assessed whether audio-haptic performance resulted in a reduction of perceptual uncertainty compared to auditory-only and haptic-only performance as predicted by maximum-likelihood estimation model. We then compared how this ability develops in 28 children and adults with different levels of visual experience, focussing on low-vision individuals and blind individuals that lost their sight at different ages during development. Our results show that in sighted individuals, adult-like audio-haptic integration develops around 13-15years of age, and remains stable until late adulthood. While early-blind individuals, even at the youngest ages, integrate audio-haptic information in an optimal fashion, late-blind individuals do not. Optimal integration in low-vision individuals follows a similar developmental trajectory as that of sighted individuals. These findings demonstrate that visual experience is not necessary for optimal audio-haptic integration to emerge, but that consistency of sensory information across development is key for the functional outcome of optimal multisensory integration.

Two Forms of Knowledge Representations in the Human Brain

Sensory experience shapes what and how knowledge is stored in the brain-our knowledge about the color of roses depends in part on the activity of color-responsive neurons based on experiences of seeing roses. We compared the brain basis of color knowledge in congenitally (or early) blind individuals, whose color knowledge can only be obtained through language descriptions and/or cognitive inference, to that of sighted individuals whose color-knowledge benefits from both sensory experience and language. We found that some regions support color knowledge only in the sighted, whereas a region in the left dorsal anterior temporal lobe supports object-color knowledge in both the blind and sighted groups, indicating the existence of a sensory-independent knowledge coding system in both groups. Thus, there are (at least) two forms of object knowledge representations in the human brain: sensory-derived and language- and cognition-derived knowledge, supported by different brain systems.

What and where in the auditory systems of sighted and early blind individuals: Evidence from representational similarity analysis

Separated ventral and dorsal streams in auditory system have been proposed to process sound identification and localization respectively. Despite the popularity of the dual-pathway model, it remains controversial how much independence two neural pathways enjoy and whether visual experiences can influence the distinct cortical organizational scheme. In this study, representational similarity analysis (RSA) was used to explore the functional roles of distinct cortical regions that lay within either the ventral or dorsal auditory streams of sighted and early blind (EB) participants. We found functionally segregated auditory networks in both sighted and EB groups where anterior superior temporal gyrus (aSTG) and inferior frontal junction (IFJ) were more related to the sound identification, while posterior superior temporal gyrus (pSTG) and inferior parietal lobe (IPL) preferred the sound localization. The findings indicated visual experiences may not have an influence on this functional dissociation and the cortex of the human brain may be organized as task-specific and modality-independent strategies. Meanwhile, partial overlap of spatial and non-spatial auditory information processing was observed, illustrating the existence of interaction between the two auditory streams. Furthermore, we investigated the effect of visual experiences on the neural bases of auditory perception and observed the cortical reorganization in EB participants in whom middle occipital gyrus was recruited to process auditory information. Our findings examined the distinct cortical networks that abstractly encoded sound identification and localization, and confirmed the existence of interaction from the multivariate perspective. Furthermore, the results suggested visual experience might not impact the functional specialization of auditory regions.

Categorical representation from sound and sight in the ventral occipito-temporal cortex of sighted and blind.

Is vision necessary for the development of the categorical organization of the Ventral Occipito-Temporal Cortex (VOTC)? We used fMRI to characterize VOTC responses to eight categories presented acoustically in sighted and early blind individuals, and visually in a separate sighted group. We observed that VOTC reliably encodes sound categories in sighted and blind people using a representational structure and connectivity partially similar to the one found in vision. Sound categories were, however, more reliably encoded in the blind than the sighted group, using a representational format closer to the one found in vision. Crucially, VOTC in blind represents the categorical membership of sounds rather than their acoustic features. Our results suggest that sounds trigger categorical responses in the VOTC of congenitally blind and sighted people that partially match the topography and functional profile of the visual response, despite qualitative nuances in the categorical organization of VOTC between modalities and groups.

Enhanced auditory segregation in early blind individuals

Enhanced auditory segregation in early blind individuals

Pain Hypersensitivity is Associated with Increased Amygdala Volume and c-Fos Immunoreactivity in Anophthalmic Mice.

It is well established that early blindness results in brain plasticity and behavioral changes in both humans and animals. However, only a few studies have examined the effects of blindness on pain perception. In these studies, pain hypersensitivity was reported in early, but not late, blind humans. The underlying mechanisms remain unclear, but considering its key role in pain perception and modulation, the amygdala may contribute to this pain hypersensitivity. The first aim of this study was to develop an animal model of early blindness to examine the effects of blindness on pain perception. A mouse cross was therefore developed (ZRDBA mice), in which half of the animals are born sighted and half are born anophthalmic, allowing comparisons between blind and sighted mice with the same genetic background. The second aim of the present study was to examine mechanical and thermal pain thresholds as well as pain behaviors and pain-related c-Fos immunoreactivity induced by the formalin test in the amygdalas of blind and sighted mice. Group differences in amygdala volume were also assessed histologically. Blind mice exhibited lower mechanical and thermal pain thresholds and more pain behaviors during the acute phase of the formalin test, compared with sighted mice. Moreover, pain hypersensitivity during the formalin test was associated with increased c-Fos immunoreactivity in the amygdala. Furthermore, amygdala volume was larger bilaterally in blind compared with sighted mice. These results indicate that congenitally blind mice show pain hypersensitivity like early blind individuals and suggest that this is due in part to plasticity in the amygdala.

Responses in area hMT+ reflect tuning for both auditory frequency and motion after blindness early in life

Previous studies report that human middle temporal complex (hMT+) is sensitive to auditory motion in early-blind individuals. Here, we show that hMT+ also develops selectivity for auditory frequency after early blindness, and that this selectivity is maintained after sight recovery in adulthood. Frequency selectivity was assessed using both moving band-pass and stationary pure-tone stimuli. As expected, within primary auditory cortex, both moving and stationary stimuli successfully elicited frequency-selective responses, organized in a tonotopic map, for all subjects. In early-blind and sight-recovery subjects, we saw evidence for frequency selectivity within hMT+ for the auditory stimulus that contained motion. We did not find frequency-tuned responses within hMT+ when using the stationary stimulus in either early-blind or sight-recovery subjects. We saw no evidence for auditory frequency selectivity in hMT+ in sighted subjects using either stimulus. Thus, after early blindness, hMT+ can exhibit selectivity for auditory frequency. Remarkably, this auditory frequency tuning persists in two adult sight-recovery subjects, showing that, in these subjects, auditory frequency-tuned responses can coexist with visually driven responses in hMT+.

Adults' visual recognition of actions simulations by finger gestures (ASFGs) produced by sighted and blind individuals.

The present study examines the visual recognition of action simulations by finger gestures (ASFGs) produced by sighted and blind individuals. In ASFGs, fingers simulate legs to represent actions such as jumping, spinning, climbing, etc. The question is to determine whether the common motor experience of one’s own body is sufficient to produce adequate ASFGs or whether the possibility to see gestures from others are also necessary to do it. Three experiments were carried out to address this question. Experiment 1 examined in 74 sighted adults the recognition of 18 types of ASFGs produced by 20 blindfolded sighted adults. Results showed that rates of correct recognition were globally very high, but varied with the type of ASFG. Experiment 2 studied in 91 other sighted adults the recognition of ASFGs produced by 10 early blind and 7 late blind adults. Results also showed a high level of recognition with a similar order of recognizability by type of ASFG. However, ASFGs produced by early blind individuals were more poorly recognized than those produced by late blind individuals. In order to match data of recognition obtained with the form that gestures are produced by individuals, two independant judges evaluated prototypical and atypical attributes of ASFG produced by blindfolded sighted, early blind and late blind individuals in Experiment 3. Results revealed the occurrence of more atypical attributes in ASFG produced by blind individuals: their ASFGs transpose more body movements from a character-viewpoint in less agreement with visual rules. The practical interest of the study relates to the relevance of including ASFGs as a new exploratory procedure in tactile devices which are more apt to convey action concepts to blind users/readers.

Distinctive Interaction Between Cognitive Networks and the Visual Cortex in Early Blind Individuals.

In early blind individuals, brain activation by a variety of nonperceptual cognitive tasks extends to the visual cortex, while in the sighted it is restricted to supramodal association areas. We hypothesized that such activation results from the integration of different sectors of the visual cortex into typical task-dependent networks. We tested this hypothesis with fMRI in blind and sighted subjects using tasks assessing speech comprehension, incidental long-term memory and both verbal and nonverbal executive control, in addition to collecting resting-state data. All tasks activated the visual cortex in blind relative to sighted subjects, which enabled its segmentation according to task sensitivity. We then assessed the unique brain-scale functional connectivity of the segmented areas during resting state. Language-related seeds were preferentially connected to frontal and temporal language areas; the seed derived from the executive task was connected to the right dorsal frontoparietal executive network; and the memory-related seed was uniquely connected to mesial frontoparietal areas involved in episodic memory retrieval. Thus, using a broad set of language, executive, and memory tasks in the same subjects, combined with resting state connectivity, we demonstrate the selective integration of different patches of the visual cortex into brain-scale networks with distinct localization, lateralization, and functional roles.

Properties of cross-modal occipital responses in early blindness: An ALE meta-analysis.

Cross-modal occipital responses appear to be essential for nonvisual processing in individuals with early blindness. However, it is not clear whether the recruitment of occipital regions depends on functional domain or sensory modality. The current study utilized a coordinate-based meta-analysis to identify the distinct brain regions involved in the functional domains of object, spatial/motion, and language processing and the common brain regions involved in both auditory and tactile modalities in individuals with early blindness. Following the PRISMA guidelines, a total of 55 studies were included in the meta-analysis. The specific analyses revealed the brain regions that are consistently recruited for each function, such as the dorsal fronto-parietal network for spatial function and ventral occipito-temporal network for object function. This is consistent with the literature, suggesting that the two visual streams are preserved in early blind individuals. The contrast analyses found specific activations in the left cuneus and lingual gyrus for language function. This finding is novel and suggests a reverse hierarchical organization of the visual cortex for early blind individuals. The conjunction analyses found common activations in the right middle temporal gyrus, right precuneus and a left parieto-occipital region. Clinically, this work contributes to visual rehabilitation in early blind individuals by revealing the function-dependent and sensory-independent networks during nonvisual processing.

Decoding auditory motion direction and location in hMT+/V5 and Planum Temporale of sighted and blind individuals

The research presented in this thesis addresses the neural mechanisms of auditory motion processing and the impact of early visual deprivation on motion-responsive brain regions, by using functional magnetic resonance imaging. Visual motion, and in particular direction selectivity, is one of the most investigated aspects of mammalian brain function. In comparison, little is known about how the brain processes moving sounds. More precisely, we have a poor understanding of how the human brain codes for the direction of auditory motion and how this process differs from auditory sound-source localization. In the first study, we characterized the neural representations of auditory motion within the Planum Temporale (PT), and how motion direction and sound source location are represented within this auditory motion responsive region. We further explore if the distribution of orientation responsive neurons (topographic representations) within the PT shares similar organizational features to what is observed within the visual motion area MT/V5. The spatial representations would, therefore, be more systematic for axis of motion/space, rather than for within-axis direction/location. Despite the shared representations between auditory spatial conditions, we show that motion directions and sound source locations generate highly distinct patterns of activity. The second study focused on the impact of early visual deprivation on auditory motion processing. Studying visual deprivation-induced plasticity sheds light on how sensory experience alters the functional organization of motion processing areas, and exploits intrinsic computational bias implemented in cortical regions. In addition to enhanced auditory motion responses within the hMT+/V5, we demonstrate that this region maintains direction selectivity tuning, but enhances its modality preference to auditory input in case of early blindness. Crucially, the enhanced computational role of hMT+/V5 is followed by a reduced role of PT for processing both motion direction and sound source location. These results suggest that early blindness triggers interplay between visual and auditory motion areas, and their computational roles could be re-distributed for effective processing of auditory spatial tasks. Overall, our findings suggest (1) auditory motion-specific processing in the typically developed auditory cortex, and (2) interplay between cross- and intra-modal plasticity to compute auditory motion and space in early blind individuals.

Early-blind Individuals Show Impaired Performance in Wine Odor Categorization

Blind individuals display superior sensory abilities in other modalities, yet results remain contradictory regarding their performance on olfactory tasks. Using complex ecological olfactory tasks, we evaluated the impact of blindness on olfactory performance. We tested 12 early-blind individuals (M = 49, SD = 13.09) and 12 sighted controls (M = 49, SD = 14.31) who were all blindfolded. Based solely on the wine odors, participants evaluated 24 pairs of wine and determined if both samples belonged to the same category (red wine, white wine, or rosé wine) or not (odor categorization), and if so, whether they were identical or not (odor differentiation). Then, they had to classify 15 different wines (5 red, 5 white and 5 rosé) into red, white, and rosé wines (odor classification). Blind individuals (d′: M = 1.3, SD = 1.2) presented lower scores compared to sighted controls (M = 2.2 SD = 0.8; p < .05) in the odor categorization task, but no group difference was observed for the other tasks. For all participants, red wine odors were the easiest to classify (1.8 ± 1.0), followed by white wine odors (0.5 ± 0.6) and finally rosé wine odors (blind and sighted; F[2; 44] = 11.9, p < .001). In summary, early-blind individuals had a harder time to categorize wine odors. This could be explained by a different construction of internal reference categories for wine in early-blind individuals. Finally, this research is in line with the notion of the absence of higher olfactory sensitivity in blind individuals.

The Effect of Blindness on Long-Term Episodic Memory for Odors and Sounds.

We recently showed that compared with sighted, early blind individuals have better episodic memory for environmental sounds, but not odors, after a short retention interval (∼ 8 – 9 min). Few studies have investigated potential effects of blindness on memory across long time frames, such as months or years. Consequently, it was unclear whether compensatory effects may vary as a function of retention interval. In this study, we followed-up participants (N = 57 out of 60) approximately 1 year after the initial testing and retested episodic recognition for environmental sounds and odors, and identification ability. In contrast to our previous findings, the early blind participants (n = 14) performed at a similar level as the late blind (n = 13) and sighted (n = 30) participants for sound recognition. Moreover, the groups had similar recognition performance of odors and identification ability of odors and sounds. These findings suggest that episodic odor memory is unaffected by blindness after both short and long retention intervals. However, the effect of blindness on episodic memory for sounds may vary as a function of retention interval, such that early blind individuals have an advantage over sighted across short but not long time frames. We speculate that the finding of a differential effect of blindness on auditory episodic memory across retention intervals may be related to different memory strategies at initial and follow-up assessments. In conclusion, this study suggests that blindness does not influence auditory or olfactory episodic memory as assessed after a long retention interval.

Enhanced perception of pitch changes in speech and music in early blind adults

It is well known that congenitally blind adults have enhanced auditory processing for some tasks. For instance, they show supra-normal capacity to perceive accelerated speech. However, only a few studies have investigated basic auditory processing in this population. In this study, we investigated if pitch processing enhancement in the blind is a domain-general or domain-specific phenomenon, and if pitch processing shares the same properties as in the sighted regarding how scores from different domains are associated. Fifteen congenitally blind adults and fifteen sighted adults participated in the study. We first created a set of personalized native and non-native vowel stimuli using an identification and rating task. Then, an adaptive discrimination paradigm was used to determine the frequency difference limen for pitch direction identification of speech (native and non-native vowels) and non-speech stimuli (musical instruments and pure tones). The results show that the blind participants had better discrimination thresholds than controls for native vowels, music stimuli, and pure tones. Whereas within the blind group, the discrimination thresholds were smaller for musical stimuli than speech stimuli, replicating previous findings in sighted participants, we did not find this effect in the current control group. Further analyses indicate that older sighted participants show higher thresholds for instrument sounds compared to speech sounds. This effect of age was not found in the blind group. Moreover, the scores across domains were not associated to the same extent in the blind as they were in the sighted. In conclusion, in addition to providing further evidence of compensatory auditory mechanisms in early blind individuals, our results point to differences in how auditory processing is modulated in this population.

The Spatial Musical Association of Response Codes does not depend on a normal visual experience: A study with early blind individuals.

Converging evidence suggests that the perception of auditory pitch exhibits a characteristic spatial organization. This pitch-space association can be demonstrated experimentally by the Spatial Musical Association of Response Codes (SMARC) effect. This is characterized by faster response times when a low-positioned key is pressed in response to a low-pitched tone, and a high-positioned key is pressed in response to a high-pitched tone. To investigate whether the development of this pitch-space association is mediated by normal visual experience, we tested a group of early blind individuals on a task that required them to discriminate the timbre of different instrument sounds with varying pitch. Results revealed a comparable pattern in the SMARC effect in both blind participants and sighted controls, suggesting that the lack of prior visual experience does not prevent the development of an association between pitch height and vertical space.

Early blindness is associated with increased volume of the uncinate fasciculus.

Growing evidence demonstrates dramatic structural and functional neuroplastic changes in individuals born with early-onset blindness. For example, cross-modal sensory processing at the level of the occipital cortex appears to be associated with adaptive behaviors in the blind. However, detailed studies examining the structural properties of key white matter pathways in other regions of the brain remain limited. Given that blind individuals rely heavily on their sense of hearing, we examined the structural properties of two important pathways involved with auditory processing, namely the uncinate and arcuate fasciculi. High angular resolution diffusion imaging (HARDI) tractography was used to examine structural parameters (i.e., tract volume and quantitative anisotropy, or QA) of these two fasciculi in a sample of 13 early blind individuals and 14 normally sighted controls. Compared to controls, early blind individuals showed a significant increase in the volume of the left uncinate fasciculus. A small area of increased QA was also observed halfway along the right arcuate fasciculus in the blind group. These findings contribute to our knowledge regarding the broad neuroplastic changes associated with profound early blindness.

Neuronal populations in the occipital cortex of the blind synchronize to the temporal dynamics of speech.

The occipital cortex of early blind individuals (EB) activates during speech processing, challenging the notion of a hard-wired neurobiology of language. But, at what stage of speech processing do occipital regions participate in EB? Here we demonstrate that parieto-occipital regions in EB enhance their synchronization to acoustic fluctuations in human speech in the theta-range (corresponding to syllabic rate), irrespective of speech intelligibility. Crucially, enhanced synchronization to the intelligibility of speech was selectively observed in primary visual cortex in EB, suggesting that this region is at the interface between speech perception and comprehension. Moreover, EB showed overall enhanced functional connectivity between temporal and occipital cortices that are sensitive to speech intelligibility and altered directionality when compared to the sighted group. These findings suggest that the occipital cortex of the blind adopts an architecture that allows the tracking of speech material, and therefore does not fully abstract from the reorganized sensory inputs it receives.

The Effect of Visual Experience on Perceived Haptic Verticality When Tilted in the Roll Plane.

The orientation of the body in space can influence perception of verticality leading sometimes to biases consistent with priors peaked at the most common head and body orientation, that is upright. In this study, we investigate haptic perception of verticality in sighted individuals and early and late blind adults when tilted counterclockwise in the roll plane. Participants were asked to perform a stimulus orientation discrimination task with their body tilted to their left ear side 90° relative to gravity. Stimuli were presented by using a motorized haptic bar. In order to test whether different reference frames relative to the head influenced perception of verticality, we varied the position of the stimulus on the body longitudinal axis. Depending on the stimulus position sighted participants tended to have biases away or toward their body tilt. Visually impaired individuals instead show a different pattern of verticality estimations. A bias toward head and body tilt (i.e., Aubert effect) was observed in late blind individuals. Interestingly, no strong biases were observed in early blind individuals. Overall, these results posit visual sensory information to be fundamental in influencing the haptic readout of proprioceptive and vestibular information about body orientation relative to gravity. The acquisition of an idiotropic vector signaling the upright might take place through vision during development. Regarding early blind individuals, independent spatial navigation experience likely enhanced by echolocation behavior might have a role in such acquisition. In the case of participants with late onset blindness, early experience of vision might lead them to anchor their visually acquired priors to the haptic modality with no disambiguation between head and body references as observed in sighted individuals (Fraser et al., 2015). With our study, we aim to investigate haptic perception of gravity direction in unusual body tilts when vision is absent due to visual impairment. Insofar, our findings throw light on the influence of proprioceptive/vestibular sensory information on haptic perceived verticality in blind individuals showing how this phenomenon is affected by visual experience.