Searching on the back:Attentional selectivity in the periphery of the tactile field

Recent evidence has identified the N140cc lateralized component of event-related potentials as a reliable index of the deployment of attention to task-relevant items in touch. However, existing ERP studies have presented the tactile search array to participants' limbs, most often to the hands. Here, we investigated distractor interference effects when the tactile search array was presented to a portion of the body that is less lateralized and peripheral compared to the hands. Participants were asked to localize a tactile target presented among distractors in a circular arrangement to their back. The N140cc was elicited contralateral to the target when the singleton distractor was absent. Its amplitude was reduced when the singleton distractor was present and contralateral to the target, suggesting that attention was directed at least in part to the distractor when the singletons are on opposite sides. However, similar N140cc were observed when the singleton distractor was ipsilateral to the target compared to distractor absent trials. We suggest that when target and singleton distractor are ipsilateral, the exact localization of the target requires the attentional processing of all items on the same side of the array, similar to distractor absent trials. Together, these observations replicate the distractor interference effects previously observed for the hands, suggesting that analogous mechanisms guide attentional selectivity across different body parts

Exploration of closing-in behaviour in dementia, development and healthy adulthood

Closing-in Behaviour (CIB) is the tendency observed in copying tasks, both graphic and gestural, in which the copy is made inappropriately close to or on top of the model. It is classically considered as a manifestation of Constructional Apraxia (CA) and it is often observed in patients with dementia. CIB is not only a symptom of pathology, but it is also observed in children’s first attempts at graphic copying. However, CIB shows an inverse pattern in development and dementia: while its frequency increases in severe dementia, CIB progressively decreases with development. The cognitive origins of CIB are still unclear. Two main interpretations dominate CIB literature: the compensation and the attraction hypotheses. The first hypothesis interprets CIB as a strategy specific to copying tasks that the patient adopts to overcome visuospatial and working memory deficits. In contrast, the attraction hypothesis considers CIB as a primitive behaviour, not specific to copying, and characterized by the default tendency to perform an action toward the focus of attention. This thesis aimed to study the characteristics and the cognitive origins of CIB in dementia, development and healthy adulthood. It has three main sections. The first and second sections explore CIB in patients (with Alzheimer’s disease- AD and Frontotemporal dementia) and in pre-school children, using survey and experimental studies, to investigate if CIB might have common characteristics and cognitive substrates in these different populations. The results provided converging evidence for the similar nature of CIB in development and dementia. For instance, survey studies in patients with dementia (Chapter 3) and preschool children (Chapter 6) showed that performance in attentional tasks predicted the appearance of CIB. In a similar vein, experimental studies showed support for the attraction hypothesis of CIB in a single patient with AD (Chapter 4) and pre-school children (Chapter 7 and 8). These results were not, however, replicated in a larger cohort of patients with AD due to practical reasons (Chapter 5). The last section was devoted to modelling CIB in normal participants, using complex graphic copying (Chapter 9) and dual task paradigms (Chapter 10). The results showed further support for the attraction hypothesis of CIB and underlined the difficulties of eliciting this default bias in normal adults. To conclude, this thesis radically changes the classical consideration of CIB as a manifestation of CA and demonstrates that CIB is a general default tendency, not specific to copying tasks. This work indicates avenues for new studies, which might consider the possible expression and consequences of this behaviour in patients’ daily lives

Closing-in Behavior in Mild Cognitive Impairment: An Executive Deficit

This study explored Closing-in behavior (CIB), the tendency in figure copying to draw very close to or on top of the model, in mild cognitive impairment (MCI). The files of 154 people diagnosed with MCI were reviewed and CIB was identified in 21% of cases. Two approaches were used to explore CIB. First, we capitalized on the diverse cognitive profiles within MCI, subdividing the overall sample into people with and without memory deficits. The frequency of CIB was significantly higher in multidomain non-amnestic MCI than in multidomain amnestic MCI, suggesting that CIB is not associated with specific memory impairment. Second, we assessed the cognitive correlates of CIB, by selecting patients with MCI who completed a battery of executive, visuo-constructional and memory tasks. Sub-groups of patients with and without CIB showed a similar overall severity of cognitive decline and comparable performance in visuo-constructional and memory tasks, but those with CIB were slightly but significantly more impaired on executive function tasks. The study provides evidence against memory-based accounts of CIB, and supports recent suggestions that executive impairments are the dominant cognitive correlate of this clinical sign

Spatially mediated interactions between singletons in tactile search

In visual search tasks competitive interactions between target and distractor typically result in degraded target selection processes which increase as the target-distractor distance decreases. Here, we investigated for the first time whether analogous selective mechanisms operate within the somatosensory system. Specifically, we investigated whether the N140cc, an ERP component known to be associated with target selection in touch, changes as function of the target-singleton distractor distance in an additional singleton search task. Six simultaneous vibro-tactile stimuli were presented on each trial to three fingers of the left and right hand. Participants were asked to localise the singleton target (high frequency stimulus) while ignoring the singleton distractor (middle frequency stimulus) delivered to a different finger of the same hand as well as the homogenous distractors (low frequency stimuli) presented to the remaining fingers. The spatial separation between target and singleton distractor was varied according to both somatotopic space (singletons to contiguous or non-contiguous fingers) and external space (fingers open or closed). Behavioural results demonstrated that accuracy improved when target and distractor were close together than far apart with respect to both somatotopic and external distance. Thus, unlike vision, competition between singletons was reduced when their distance decreased. ERP results showed that the N140cc amplitude was enhanced when the somatotopic distance between target and singleton distractor increased (non-contiguous singletons), while it was reduced when their external distance increased (fingers open). These findings confirm the N140cc as an index of target selection and further suggest that this component is able to capture and distinguish the effects of different body representations (somatosensory and external) on tactile selective attention

The attraction of emotions: Irrelevant emotional information modulates motor actions

Emotional expressions are important cues that capture our attention automatically. Although a wide range of work has explored the role and influence of emotions on cognition and behavior, little is known about the way that emotions influence motor actions. Moreover, considering how critical detecting emotional facial expressions in the environment can be, it is important to understand their impact even when they are not directly relevant to the task being performed. Our novel approach was to explore this issue from the attention-and-action perspective, using a task-irrelevant distractor paradigm in which participants are asked to reach for a target while a nontarget stimulus is also presented. We tested whether the movement trajectory would be influenced by irrelevant stimuli—faces with or without emotional expressions. The results showed that reaching paths veered toward faces with emotional expressions, in particular happiness, but not toward neutral expressions. This reinforces the view of emotions as attention-capturing stimuli that are, however, also potential sources of distraction for motor actions

Behavioural and Electrophysiological evidence for the effect of target-distractor separation in a tactile search task

Evidence suggests that the N140cc component of event-related potentials (ERP) observed in tactile search tasks reflects the attentional selection of the target. Here, we investigated whether the target selection processes are affected by the separation between the target and an ipsilateral singleton distractor (singletons delivered to contiguous or non-contiguous fingers of the same hand). In addition, the external distance between search items was varied through posture (splayed or touching fingers). Accuracy improved when target and distractor were delivered to contiguous fingers that were also touching. Regardless of target-distractor separation, the N140cc was larger when the external distance between search-array stimuli decreased (touching fingers). Importantly, a smaller N140cc was observed at reduced target-distractor separations, suggesting a narrower attentional focus for contiguous singletons. These findings reveal that the mechanisms responsible for tactile target selection in the presence of an ipsilateral singleton distractor are fundamentally different from those emerged in vision