Biomedical subjects

Lilach Shalev

Publications and source records attributed to Lilach Shalev.

7 recordsLinked to original sources

PubMed2006

Opposite biases in salience-based selection for the left and right posterior parietal cortex.

Visual selection is determined in part by the saliency of stimuli. We assessed the brain mechanisms determining attentional responses to saliency. Repetitive transcranial magnetic stimulation (rTMS) was applied to the left and right posterior parietal cortices (PPC) immediately before participants were asked to identify a compound letter. rTMS to the right PPC disrupted the guidance of attention toward salient stimuli, whereas rTMS to the left PPC affected the ability to bias selection away from salient stimuli. We conclude that right and left PPC have opposite roles in biasing selection to and from salient stimuli in the environment.

Attention↗

PubMed2005

Effects of saliency, not global dominance, in patients with left parietal damage.

Neuropsychological and functional imaging studies have shown a general right hemisphere advantage for processing global visual information and a left hemisphere advantage for processing local information. There is also evidence for the left parietal lobe being important for switching attention between local and global levels. Here we examined whether the left parietal lobe is associated with another aspect of attentional control over hierarchical visual processing; namely, ignoring the irrelevant aspect of the stimulus when it is more salient than the target attribute. In experiment 1 a group of left parietal patients were abnormally affected by a salient local stimulus that significantly interfered with their ability to identify global shapes. This effect was reversed in experiment 2 when small sized compound letters were used (where the global shape was more salient than the local letters). The patients then had difficulty ignoring the global shape. Experiments 3 and 4 demonstrated that the failure to accurately identify global form in experiment 1 could not be attributed to a difficulty in spreading attention across a large area. Finally, in experiment 4 the effect of a salient irrelevant stimulus was significantly attenuated when the irrelevant level did not map onto a response. The data indicate that damage to the left parietal lobe disrupts the ability to select attributes of stimuli that have low salience when other attributes have high salience for the task.

Adult↗

PubMed2005

Attending to local form while ignoring global aspects depends on handedness: evidence from TMS.

Our perceptions of the whole and of the parts of a visual stimulus are mediated by different brain regions. We used low-frequency transcranial magnetic stimulation (TMS) to show for the first time that opposite, homologous regions in the two hemispheres are involved in attending to local parts for left- and right-handed individuals. The brain regions that focus on the 'trees' while ignoring the 'forest' are switched as a function of handedness.

Analysis of Variance↗

PubMed2005

Interactive perceptual and attentional limits in visual extinction.

We report a case-study of YE, a 54-year-old person who suffered multiple shell injuries that caused a right-parietal lesion and left hemianopia, almost 30 years ago. We conducted 4 experiments using a basic extinction paradigm in which YE had to report single stimuli presented on the left or right or two stimuli presented simultaneously in both visual fields. We show that extinction was selectively affected both by increasing the relative perceptual salience of the contralesional stimulus and by cueing attention to the contralesional side. The effects of perceptual salience and attentional cueing interacted, with cueing being more effective when the stimuli had relatively high perceptual salience. The data are consistent with attentional and perceptual factors interacting to determine the competition between left and right side stimuli that underlies extinction.

Attention↗

PubMed2005

The lengthening effect revisited: a reply to Prinzmetal and Wilson (1997) and Masin (1999).

In the present study, the lengthening phenomenon (Tsal & Shalev, 1996), namely, the increase in perceived length of unattended lines, was reexamined in light of criticisms by Prinzmetal and Wilson (1997) and Masin (1999). Prinzmetal and Wilson suggested that the effect was not due to attentional factors but to the spatial interaction between the attended line and the cue used to direct attention. We have replicated the lengthening effect when both attended and unattended lines are preceded by cues at a nearby location, showing that the effect is not caused by spatial cues per se, but instead reflects an inherent property of the attentional system. Masin argued that the lengthening effect is not robust, because it occurs for some but not for all participants. In the present study, the lengthening effect was highly reliable, occurring for each participant for a variety of line lengths.

Attention↗

PubMedDate not supplied

The wide attentional window: a major deficit of children with attention difficulties.

The present study assessed visual selective attention in children with attention difficulties compared to age-matched, typically achieving children. We used the flanker task, which requires participants to respond to a central target flanked by distractors, and the feature and conjunction visual search, which requires participants to search for a predesignated target embedded among a variable number of distractors. The results showed that children with attention difficulties encountered major problems only when responding to a central target flanked by adjacent incongruent distractors and when searching for a conjunctive target in a high-density display. These results suggest that children with attention difficulties have a characteristic inability to restrict visual attention to a limited spatial area so as to selectively process relevant information while effectively ignoring distracting information.

Attention Deficit Disorder with Hyperactivity↗

PubMedDate not supplied

The diversity of attention deficits in ADHD: the prevalence of four cognitive factors in ADHD versus controls.

The performance of participants with attention-deficit/hyperactivity disorder (ADHD) relative to control participants was measured on four tasks uniquely assessing the functions of selective attention, executive attention, sustained attention, and orienting of attention. The results showed that deficits in sustained attention were the most pronounced, characterizing most participants with ADHD and deficits in each of the other three functions characterized more than half of these participants. Different participants with ADHD revealed different clusters of attentional deficits. These results call for a revision of leading theories of ADHD that identify the core of the pathology as a sole deficit in executive functions.

Attention↗