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Vicino all'ombra, vicino al corpo. Uno studio sperimentale della relazione fra ombra e schema corporeo
No full textTHE TIME-COURSE OF ATTENTION SHIFTS BETWEEN EXTRA-PERSONAL AND PERSONAL SPACE TRIGGERED BY BODY SHADOWS
No full textSELF-ATTRIBUTED BODY-SHADOWS MODULATE TACTILE ATTENTION
No full textOur body-shadows are special stimuli in the visual world. They often have anatomical resemblance
with our own body-parts and move as our body moves, with spatio-temporal correlation.
Here, we show that self-attributed body-shadows cue attention to the body-part they refer to,
rather than the location they occupy. Using speeded spatial discrimination for tactile or visual targets
at the hands, or for visual targets delivered near the hand-shadows, we demonstrate that mere
viewing of task-irrelevant shadows can selectively facilitate tactile discrimination at the body-part
casting the shadow (Experiment 1). In addition, such facilitation only develops through time for
cast-shadows that have no resemblance with the body-part, but move in spatio-temporal correlation
with it (Experiment 2). Conversely, facilitation fades away rapidly for shadow-like images that
resemble the stimulated body-part, but are in fact static pictures (Experiment 3). Thus, recognising
oneself as the owner of a shadow aVects distribution of tactile attention
LONG-LASTING CAPTURE OF TACTILE ATTENTION BY BODY SHADOWS
No full textFour experiments addressed the role of cast
shadows of the body in orienting tactile spatial attention
to the body itself. We used a modified spatial-cueing
paradigm to examine whether viewing of the cast shadow
of a hand can elicit spatial shifts of tactile attention
to that very same hand. Participants performed a speeded
tactile-discrimination task (thumb versus index finger,
regardless of touched hand), while viewing the
shadow of either the touched or untouched hand cast in
front of them by a lateral light-source. The hand casting
the shadow changed either between blocks (expt 1) or
unpredictably within each block (expts 2–4). In experiments
1 and 2 tactile targets were preceded by central
non-informative visual cues delivered near the shadow
of the index finger and thumb. Despite the fact that cast
shadows were always task-irrelevant and non-predictive
of which hand was stimulated, tactile discrimination was
consistently faster at the hand casting the shadow than
at the other hand. This effect was not modulated by the
duration of cue-target asynchrony, nor did it depend on
whether the visual cue was present or not (expt 3). In
addition, it was still reliable when vision of the hands
was precluded, whereas it became inconsistent when the
cast shadow of the hand was replaced by the cast shadow
of an object (expt 4). Our results suggest that body
shadows can induce a long-lasting capture of tactile
attention for stimuli at the body itself
Poor hand-pointing to sounds in right brain-damaged patients: Not just a problem of spatial-hearing.
No full textWe asked 22 right brain-damaged (RBD) patients and 11 elderly healthy controls to perform hand-pointing movements to free-field unseen sounds, while modulating two non-auditory variables: the initial position of the responding hand (left, centre or right) and the presence or absence of task-irrelevant ambient vision. RBD patients suffering from visual neglect, unlike RBD patients without neglect and healthy controls, showed a systematic rightward error in sound localisation, which was modulated by the non-auditory variables. Localisation errors were exacerbated by initial hand-position to the right of the body-midline, and reduced by the leftwards initial hand-position. Moreover, for the visual neglect patients, mere presence of ambient vision worsened localisation errors. These results demonstrate that although hand-pointing to sounds has often been considered a straightforward approach to investigate sound-localisation abilities in brain-damaged patients, in some patients it may actually reveal localisation deficits that reflect a combination of impaired spatial-hearing and spatial biases from other sensory modalities (i.e., vision and proprioception)
Gaze direction modulates auditory spatial deficits in stroke patients with neglect.
No full textWe investigated the effects of eye position on auditory spatial deficits in four patients with left neglect and right-hemisphere damage, using three blocked gaze directions (35 degrees to the right, central, or 35 degrees to the left), while preventing any head-movement to ensure that initial auditory inputs remained constant regardless of eye-in-orbit position. The auditory task required speeded discrimination of sound elevation, with patients moving a central lever up or down according to the vertical position of a peripheral target sound, regardless of its side (left or right). Replicating previous auditory research, the patients' vertical discrimination performance was worse for auditory targets on the contralesional (left) versus the ipsilesional side, indicating neglect-related auditory deficits on this task. Critically, while this worse performance for left than right auditory targets was present (for both reaction times and errors) when gaze was directed centrally or rightwards, it was considerably reduced when gaze was directed leftwards. These results demonstrate that lateral gaze-direction can modulate neglect-related auditory spatial deficits, even though eye-position did not alter the initial auditory inputs. This outcome may relate to audio-visual links in spatial orienting and potentially some retinocentric influences on perceived sound location, although the latter alone could not explain all our results. Such findings might involve multisensory brain structures in which responses to sounds are modulated by eye-in-orbit position
Changing auditory time with prismatic goggles
No full textThe aim of the present study was to explore the spatial organization of auditory time and
the effects of the manipulation of spatial attention on such a representation. In two experiments,
we asked 28 adults to classify the duration of auditory stimuli as ‘‘short’’ or ‘‘long’’.
Stimuli were tones of high or low pitch, delivered left or right of the participant. The time
bisection task was performed either on right or left stimuli regardless of their pitch (Spatial
experiment), or on high or low tones regardless of their location (Tonal experiment). Duration
of left stimuli was underestimated relative to that of right stimuli, in the Spatial but
not in the Tonal experiment, suggesting that a spatial representation of auditory time
emerges selectively when spatial-encoding is enforced. Further, when we introduced spatial-
attention shifts using the prismatic adaptation procedure, we found modulations of
auditory time processing as a function of prismatic deviation, which correlated with the
interparticipant adaptation effect. These novel findings reveal a spatial representation of
auditory time, modulated by spatial attention
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