Biomedical subjects

Alessandro Couyoumdjian

Publications and source records attributed to Alessandro Couyoumdjian.

5 recordsLinked to original sources

PubMed2006

Audio-visual dynamic remapping in an endogenous spatial attention task.

Several studies on cross-modal attention showed that remapping processes between sensory modalities occur in the spatial orienting of attention. One hypothesis that accounts for such links is that spatial attention operates upon representations of common locations in the external space. However, convincing evidence only exists for cross-modal links in spatial orienting, leaving the dynamics of these effects unexplored. Four experiments were designed to cope with this issue by having participants being involved in an endogenous orienting task to visual and auditory target stimuli. Targets on invalid trials were embedded into two different kinds of sequences of stimuli: (1) long sequences, wherein three valid trials in one modality preceded the invalid trial in the other modality; (2) short sequences, wherein only one valid trial in one modality preceded the invalid trial in the other modality. Results revealed modality-specific meridian effects in the short sequences, and a significant decrement of the modality-specific meridian effect in the long sequences. The results of these experiments indicate that cross-modal links in visual and auditory spatial attention are based on representations of common locations in the external space across sensory modalities. Moreover, the results strongly support the hypothesis that representations of space are dynamically built and updated according to task demands.

Acoustic Stimulation↗

PubMed2006

Crossing the pillars of Hercules: the role of spatial frames of reference in error making.

This paper introduces a perspective accounting for errors that may occur as a result of the human interaction with the three-dimensional (3D) space. Particularly, we are interested in errors that are caused by cognitively crossing the boundary between peripersonal and extrapersonal space. Several behavioural, neurophysiological, and neuropsychological perspectives are reviewed in order to develop the theoretical framework on which our ideas are founded. We argue that cognitively crossing the boundary implies switching from one frame of reference to another, which, as a consequence, implies specific costs. The results of five experiments (overall involving 76 participants) support our hypothesis, suggesting the existence of different action-oriented spatial frames of reference.

Adult↗

PubMed2005

Can an inert sleeping pill affect sleep? Effects on polysomnographic, behavioral and subjective measures.

RATIONALE: Since two recent meta-analyses on sleep changes associated with placebo in clinical trials suggested a beneficial effect of placebo treatments, pointing to a dissociation between subjective and objective measures of sleep, the current experiment was directly aimed to assess the effects of an inert compound, administered with the suggestion that it was a hypnotic substance in subjects with mild sleep complaints. OBJECTIVES: The aim of this study was to compare subjective, behavioral, polysomnographic (PSG), and quantitative electroencephalographic (EEG) changes during a night preceded or not by the intake of two 50-mg lactose capsules. METHODS: Ten female students, selected by the Pittsburgh Sleep Quality Index, slept for three consecutive nights in a sleep laboratory, with the experimental (EXP) night defined by the administration of two 50-mg lactose pills. Self-ratings of sleep quality and performance were assessed upon morning awakening of baseline (BSL) and EXP nights. RESULTS: The EXP nights were self-rated as more restful and characterized by a decreased number of nocturnal awakenings than the BSL nights. PSG measures showed that wakefulness after sleep onset significantly decreased during the EXP night as compared to the BSL night. The EXP nights also showed an increase of 0.5-4.0 Hz power during nonrapid eye movement sleep and a decrease of EEG activity in the beta frequency range during rapid eye movement sleep only at central brain sites. A specific improvement of behavioral measures was also found upon morning awakening after the EXP night compared to the BSL night. CONCLUSIONS: The administration of an inert pill improves both the subjective and objective quality of sleep. The reduced sleep fragmentation and the effects on some quantitative EEG markers of sleep homeostasis suggest that the experimental manipulation induced coherent changes in the subsequent sleep, resembling an enhancement of sleep pressure. The regional differences of EEG activity suggest the involvement of a specific physiological mechanism distinct from that of effective treatments.

Adult↗

PubMed2004

Opposite visual field asymmetries for egocentric and allocentric spatial judgments.

The purpose of the present study was to investigate the relation between visual hemifields and spatial frames of reference, according to the idea that multiple representations of 3D space exist. Results from two experiments clearly show that an upper visual hemifield advantage only arises when allocentric spatial judgments are required in order to perform a location task, whereas a lower visual hemifield advantage arises when egocentric spatial judgments are required. Such a double dissociation was interpreted as due to the activity of two separate neural pathways operating specific transformations of visual input for different functional outputs: scene recognition, mostly relying on allocentric frames of reference and subserved by the ventral, occipito-temporal pathway of the visual system, and goal directed actions, mostly relying on egocentric systems and subserved by the dorsal, occipito-parietal pathway of the visual system.

Adult↗

PubMed2003

Functional representation of 3D space in endogenous attention shifts.

The aim of this study was to explore whether the attentional system, as far as an endogenous orienting is concerned, allocates resources along the sagittal plane and whether such a process is affected by, and is likely to be based on, different functional representations of 3D space in the brain. Several models make a main action-based distinction between representations of peripersonal space and of those extrapersonal space. Accordingly, if attention has to move from one representation to another, it should be possible to observe a decrease in performance during such a transition. To test this hypothesis three experiments were run in which participants performed a cued detection task. Cue stimuli were informative and were centrally located around the fixation point. Target stimuli were displayed at four different depth planes. In the first experiment, assuming that the border between the peripersonal space and the extrapersonal space was at 1 m from the observer, half the target stimuli were located in the peripersonal space and half in the extrapersonal space. The fixation point was located at 1 m from the observer. In the second experiment, the fixation point was moved at 2 m from the observer in order to rule out the possible effects of ocular motor programming. In the third experiment, in order to rule out effects related to the spatial layout of target stimuli (i.e., centre of mass effect) two target stimuli were located in the peripersonal space and six in the extrapersonal space. In all the experiments, besides a validity effect, we observed greater reaction times when attention shift was across spatial representations than when it was within the same representation. The implications for action-oriented models of attention are discussed.

Adult↗