Achille Pasqualotto

The role of visual experience for the neural basis of spatial cognition

Blindness often results in the adaptive neural reorganization of the remaining modalities, producing sharper auditory and haptic behavioral performance. Yet, non-visual modalities might not be able to fully compensate for the lack of visual experience as in the case of congenital blindness. For example, developmental visual experience seems to be necessary for the maturation of multisensory neurons for spatial tasks. Additionally, the ability of vision to convey information in parallel might be taken into account as the main attribute that cannot be fully compensated by the spared modalities. Therefore, the lack of visual experience might impair all spatial tasks that require the integration of inputs from different modalities, such as having to represent a set of objects on the basis of the spatial relationships among the objects, rather than the spatial relationship that each object has with oneself. Here we integrate behavioral and neural evidence to conclude that visual experience is necessary for the neural development of normal spatial cognition.

Congenital blindness improves semantic and episodic memory.

Previous studies reported that congenitally blind people possess superior verb-generation skills. Here we tested the impact of blindness on capacity and the fidelity of semantic memory by using a false memory paradigm. In the Deese-Roediger-McDermott paradigm, participants study lists of words that are all semantically related to a lure that is not presented. Subsequently, participants frequently recall the missing lure. We found that congenitally blind participants have enhanced memory performance for recalling the presented words and reduced false memories for the lure. The dissociation of memory capacity and fidelity provides further evidence for enhanced verbal ability in the blind, supported by their broader structural and functional brain reorganisation.

Two-Dimensional Rubber-Hand Illusion: The Dorian Gray Hand Illusion.

The rubber-hand illusion provides a window into body representation and consciousness. It has been found that body-ownership extended to numerous hand-like objects. Interestingly, the vast majority of these objects were three-dimensional. We adopted this paradigm by using hand drawings to investigate whether rubber-hand illusion could be extended to two-dimensional hand samples, and we measured skin conductance responses and behavioural variables. The fact that this illusion extended to two-dimensional stimuli reveals the dominant role of top-down information on visual perception for body representation and consciousness.

The study of blindness and technology can reveal the mechanisms of three-dimensional navigation

Jeffery et al. suggest that three-dimensional environments are not represented according to their volumetric properties, but in a quasi-planar fashion. Here we take into consideration the role of visual experience and the use of technology for spatial learning to better understand the nature of the preference of horizontal over vertical spatial representation.

Neural Stimulation Has a Long-Term Effect on Foreign Vocabulary Acquisition

Acquisition of a foreign language is a challenging task that is becoming increasingly more important in the world nowadays. There is evidence suggesting that the frontal and temporal cortices are involved in language processing and comprehension, but it is still unknown whether foreign language acquisition recruits additional cortical areas in a causal manner. For the first time, we used transcranial random noise stimulation on the frontal and parietal brain areas, in order to compare its effect on the acquisition of unknown foreign words and a sham, or placebo, condition was also included. This type of noninvasive neural stimulation enhances cortical activity by boosting the spontaneous activity of neurons. Foreign vocabulary acquisition was tested both immediately and seven days after the stimulation. We found that stimulation on the posterior parietal, but not the dorsolateral prefrontal cortex or sham stimulation, significantly improved the memory performance in the long term. These results suggest that the posterior parietal cortex is directly involved in acquisition of foreign vocabulary, thus extending the “linguistic network” to this area.

The role of visual experience for spatial numerical associations

The topographic representation of space interacts with the mental representation of number. Evidence for such number–space relations have been reported in both synaesthetic and non-synaesthetic participants. Thus far most studies have only examined related effects in sighted participants. For example, the mental number line increases in magnitude from left to right in sighted individuals (Loetscher et al., 2008, Curr. Biol.). What is unclear is whether this association arises from innate mechanisms or requires visual experience early in life to develop in this way. Here we investigated the role of visual experience for the left to right spatial numerical association using a random number generation task in congenitally blind, late blind, and blindfolded sighted participants. Participants orally generated numbers randomly whilst turning their head to the left and right. Sighted participants generated smaller numbers when they turned their head to the left than to the right, consistent with past results. In contrast, congenitally blind participants generated smaller numbers when they turned their head to the right than to the left, exhibiting the opposite effect. The results of the late blind participants showed an intermediate profile between that of the sighted and congenitally blind participants. Visual experience early in life is therefore necessary for the development of the spatial numerical association of the mental number line.

Visual loss alters multisensory face maps in humans

Topographically organised responses to visual and tactile stimulation are aligned in the ventral intraparietal cortex. The critical biological importance of this region, which is thought to mediate visually guided defensive movements of the head and upper body, suggests that these maps might be hardwired from birth. Here, we investigated whether visual experience is necessary for the creation and positioning of these maps by assessing the representation of tactile stimulation in congenitally and totally blind participants, who had no visual experience, and late and totally blind participants. We used a single-subject approach to the analysis to focus on the potential individual differences in the functional neuroanatomy that might arise from different causes, durations and sensory experiences of visual impairment among participants. The overall results did not show any significant difference between congenitally and late blind participants; however, single-subject trends suggested that visual experience is not necessary to develop topographically organised maps in the intraparietal cortex, whilst losing vision disrupted topographic maps’ integrity and organisation. These results discussed in terms of brain plasticity and sensitive periods.

Mechanisms of short-term false memory formation -

False memories are the erroneous recollection of events that did not actually occur. False memories have been broadly investigated within the domain of long-term memory, while studies involving short-term memory are less common and provide a far less detailed ‘picture’ of this phenomenon. We tested participants in a short-term memory task involving lists of four semantically related words that had to be matched with a probe word. Crucially, the probe word could be one of the four words of the list, it could be semantically related to them, or it could be semantically unrelated to the list. Participants had to decide whether the probe was in the list. To this task we added articulatory suppression to impair rehearsal, concurrent material to remember, and changes to the visual appearance of the probes to assess the mechanism involved in short-term memory retrieval. The results showed that, similarly to the studies on long-term memory, false memories emerged more frequently for probes semantically related to the list and when rehearsal was impaired by concurrent material. The visual appearance of the stimuli did not play an important role. This set of results suggests that deep semantic processing, rather than only superficial visual processing, is taking place within a few seconds from the presentation of the probes.

Visual experience and the establishment of spatial and tactile maps in the brain

Visual experience is necessary for the normal development of spatial cognition. Although some aspects of spatial processing in an egocentric reference frame are well preserved in the case of congenital blindness, it appears the lack of vision influences processing in an allocentric reference frame. Here I will first report our finding that visual experience biases congenitally blind participants to rely on an egocentric reference frame for spatial cognition tasks, rather than an allocentric reference frame that is favoured by late blind and sighted participants. This suggests that visual experience can influence the neural basis of spatial representations, given the importance of vision for normal multisensory processing. A previous study discovered an area in human parietal cortex with aligned maps of tactile and visual stimuli. We investigated whether visual experience is necessary for the development of tactile maps in multisensory areas, such as the putative human ventral intraparietal (VIP) area reported previously. Congenital and late blind participants underwent functional magnetic resonance imaging while exposed to facial air-puffs of varying polar angle. Phase-encoding of the facial air-puffs allowed for tactile mapping that revealed full face maps in the posterior parietal cortex of the late blind participants, as reported previously for sighted participants. The congenitally blind participants however did not have the same representation of the face map as those with visual experience. Retinotopic maps are ideal for characterizing an allocentric representation of the environment and might be necessary as the basis for representing and aligning the neural representation of space as seen in the somatotopic maps examined here.

The role of visual experience in spatial reference frame preference

How do people remember the location of objects? Location is always relative, and thus depends on a reference frame. There are two types of reference frames: egocentric (or observer-based) and allocentric (or environmental-based). Here we investigated the reference frame people used to remember object locations in a large room. We also examined whether the choice of a given reference frame is dictated by visual experience. Thus we tested congenitally blind, late blind, and sighted blindfolded participants. Objects were organized in a structured configuration and then explored one-by-one with participants walking back and forth from a single point. After the exploration of the locations, a spatial memory test was conducted. The memory test required participants to imagine being inside the array of objects, being oriented along a given heading, and then pointing towards the required object. Crucially the headings were either aligned to the allocentric structure of the configuration, that is rows and columns, or aligned to the egocentric route walked during the exploration of the objects. The spatial representation used by the participants can be revealed by better performance when the imagined heading in the test matches the spatial representation used. We found that participants with visual experience, that is late blind and blindfolded sighted, were better with headings aligned to the allocentric structure of the configuration. On the contrary, congenitally blind were more accurate with headings aligned to the egocentric walked routes. This suggests that visual experience during early development determines a preference for an allocentric frame of reference.