Tell it to the hand: Attentional modulation in the identification of misoriented chiral objects

Research in the field of cognitive neuroscience and neuropsychology on spatial cognition and mental imagery has increased considerably over the last few decades. While at the beginning of the XX century studying imagery was considered an object of derision – a ―sheer bunk‖ (Watson, 1928) – at the present, imagery researchers have successfully developed models and improved behavioral and neurophysiological measures (e.g., Kosslyn et al., 2006). Mental rotation constituted a major advance in terms of behavioral measures sensitive to imaginative operations executed on visual representations (i.e., Shepard & Cooper, 1982). The linearity of modulation between response times and angular disparity of the images allowed a quantitative estimate of imagery processes. The experiments described in the present thesis were motivated by the intent to continue and extend the understanding of such fascinating mental phenomena. The evolution of the present work took initial steps from the adoption of a behavioral paradigm, the hand laterality judgment task, as privileged tool for studying motor imagery in healthy individuals and brain-damaged patients. The similarity with mental rotation tasks and the implicit nature of the task made it the best candidate to test hypotheses regarding the mental simulation of body movements. In this task, response times are linearly affected by the angular departures the hand pictures are shown in, as for mental rotation, and their distributions are asymmetric between left and right hands. Drawing from these task features a widely held view posits that laterality judgment of rotated hand pictures requires participants to imagine hand-arm movements, although they receive no instruction to do so (e.g., Parsons, 1987a; Parsons, 1994). In Chapter 1, I provided a review of the relevant literature on visual and motor imagery. Particular aspects of the mental rotation literature are also explored. In Chapter 2, I examined the hand laterality task and the vast literature of studies that employed this task as means to test motor imagery processes. An alternative view to the motor imagery account is also discussed (i.e., the disembodied account). In Chapter 3, I exploited the hand laterality task, and a visual laterality task (Tomasino et al., 2010) to test motor and visual imagery abilities in a group of healthy aged individuals. In Chapter 4, I described an alternative view that has been proposed by others to explain the pattern of RTs in the hand laterality task: The multisensory integration account (Grafton & Viswanathan, 2014). In this view, hand laterality is recognized by pairing information between the seen hand's visual features and the observer's felt own hand. In Chapter 5, I tested and found evidence for a new interpretation of the particular configuration of response times in the hand laterality task. I demonstrated a spatial compatibility effect for rotated pictures of hands given by the interaction between the direction of stimulus rotation (clockwise vs. counterclockwise) and the laterality of the motor response. These effects changed by following temporal dynamics that were attributed to shifts of spatial attention. In the same chapter, I conducted other psychophysics experiments that confirmed the role of spatial attention and that ruled out the view of multisensory integration as the key aspect in determining the asymmetries of the response times' distribution. In Chapter 6, I conducted a study with patients suffering from Unilateral Neglect in which they performed the hand laterality task and a visual laterality task. The findings indicated that patients failed to integrate visual information with spatially incompatible responses irrespective of the type of task, and depending on egocentric stimulus-response spatial codes. A general discussion is presented in Chapter 7.