Sunday, October 02nd, 2011 [17:00 - 18:00]
OS_43.1 - The bisection of words and lines depends on different mechanisms: Evidence from spatial neglect
Veronelli, L. 1, 2 , Vallar, G. 1, 3 , Marinelli, C. V. 4, 5 , Primativo, S. 4, 5 & Arduino, L. S. 6, 7
1 Department of Psychology, University of Milano-Bicocca, Milan, Italy
2 Department of Neuro Rehabilitative Sciences, Casa Di Cura Privata del Policlinico, Milan, Italy
3 IRCCS Istituto Auxologico Italiano, Milan, Italy
4 Department of Psychology, University of Rome La Sapienza, Rome, Italy
5 Neuropsychological Research Centre, IRCCS Foundation Hospital Santa Lucia, Rome, Italy
6 Department Of Psychology, LUMSA University, Rome, Italy
7 ISTC-CNR, Rome, Italy
In a line bisection task, right-brain damaged patients with unilateral spatial neglect (USN) set the midline to the right with respect to the objective midpoint, while unimpaired participants (UP) show a reversed bias (‘pseudoneglect’). In a recent study with UP, Arduino, Previtali and Girelli (2010) demonstrated that length differently affects the bisection of lines and orthographic stimuli, suggesting that different mechanisms may be involved in word and line bisection. The present study investigated these stimulus-dependent biases in USN patients. In Experiment 1 eleven patients and matched controls were asked to bisect words of different lengths (5-13 letters) and comparable lines. Experiment 2 focused on ortho-phonological features, requiring the bisection of words with different final sequences (stressed on the penultimate or antepenultimate syllable). Despite an overall rightward error modulated by stimulus length, in a few patients the directional biases for words and lines conjured up a double dissociation (Exp. 1), supporting the existence of partially independent mechanisms in word and line bisection. Results from Experiment 2 indicate that the final part of a word could be used by USN patients as a cue during bisection. Globally, both visuo-spatial and lexical mechanisms seem to influence the bisection of word in USN patients.
OS_43.2 - Attention to within-string position in letter-in-string identification
Marzouki, Y. 1 , Jouanin, M. 2 & Grainger, J. 3
1 Aix-Marseille University & CNRS
2 Aix-Marseille University
Two experiments combined exogenous spatial cueing with a letter-in-string identification task in order to examine whether attention could be directed to within-word position independently of retinal location. In Experiment 1, a spatial cue appeared in one of three horizontally aligned boxes mimicking the spatial layout of 3-letter target strings. Cues could be at the same within-string position as the target letter, or at one of the two other positions. Spatial overlap was manipulated by having targets aligned with the boxes, displaced to the left or to the right, or by reducing inter-letter spacing. Spatial cueing effects were found to be driven uniquely by within-string position independently of spatial overlap. Experiment 2 demonstrated that spatial cueing effects disappeared in the displaced and squashed conditions when the boxes were removed, confirming that attention to within-string position was driving the effects in these conditions in Experiment 1. This pattern suggests a key role for object-based attention in letter-in-string identification.
OS_43.3 - Covert and overt inhibition of return in ventral and dorsal brain regions
Bourgeois, A. 1 , Chica, A. 1 , Migliaccio, R. 1, 3 , Thiebaut de Schotten, M. 1, 4 , Valero Cabre, A. 1 & Bartolomeo, P. 1, 2, 3
1 Inserm-UPMC UMRS975
2 AP-HP, Groupe hospitalier Pitié-Salpêtrière, Paris, France
3 Department of Psychology, Catholic University, Milan, Italy
4 Natbrainlab, Department of Forensic and Neurodevelopmental Sciences, Institute of Psychiatry, King's College, London, UK
When two consecutive events appear at the same spatial location, responses to the second event are slower than those to the first. This effect, known as inhibition of return (IOR), reflects a bias to preferentially attend to novel locations, which is necessary to explore our environment efficiently. We demonstrate that patients with right brain damage and left neglect present an impaired IOR under cover orienting situations, while saccadic IOR (overt orienting) is preserved (Bourgeois et al., under review). Neuroanatomical data demonstrate that all neglect patients with impaired covert IOR presented parietal damage or fronto-parietal disconnection. We used then an off-line repetitive Transcranial Magnetic Stimulation (rTMS) to determine the role of two parietal regions (right intraparietal sulcus -IPS, and right temporo-parietal junction -TPJ) in covert and overt IOR in healthy participants. We demonstrate that TMS over TPJ replicates IOR impairments observed in neglect patients. TMS over IPS affects both covert and overt orienting. Understanding the neural basis of covert and overt IOR is crucial for understanding attentional orienting and their underlying neural mechanisms in both the healthy and damaged brain.