Biomedical subjects

Leonardo Chelazzi

Publications and source records attributed to Leonardo Chelazzi.

4 recordsLinked to original sources

PubMed2004

Attentional modulation of visual processing.

Single-unit recording studies in the macaque have carefully documented the modulatory effects of attention on the response properties of visual cortical neurons. Attention produces qualitatively different effects on firing rate, depending on whether a stimulus appears alone or accompanied by distracters. Studies of contrast gain control in anesthetized mammals have found parallel patterns of results when the luminance contrast of a stimulus increases. This finding suggests that attention has co-opted the circuits that mediate contrast gain control and that it operates by increasing the effective contrast of the attended stimulus. Consistent with this idea, microstimulation of the frontal eye fields, one of several areas that control the allocation of spatial attention, induces spatially local increases in sensitivity both at the behavioral level and among neurons in area V4, where endogenously generated attention increases contrast sensitivity. Studies in the slice have begun to explain how modulatory signals might cause such increases in sensitivity.

Action Potentials↗

PubMed2003

Associative knowledge controls deployment of visual selective attention.

According to some models of visual selective attention, objects in a scene activate corresponding neural representations, which compete for perceptual awareness and motor behavior. During a visual search for a target object, top-down control exerted by working memory representations of the target's defining properties resolves competition in favor of the target. These models, however, ignore the existence of associative links among object representations. Here we show that such associations can strongly influence deployment of attention in humans. In the context of visual search, objects associated with the target were both recalled more often and recognized more accurately than unrelated distractors. Notably, both target and associated objects competitively weakened recognition of unrelated distractors and slowed responses to a luminance probe. Moreover, in a speeded search protocol, associated objects rendered search both slower and less accurate. Finally, the first saccades after onset of the stimulus array were more often directed toward associated than control items.

Adolescent↗

PubMed2002

My eyes want to look where your eyes are looking: exploring the tendency to imitate another individual's gaze.

In this study we investigated the tendency of humans to imitate the gaze direction of other individuals. Distracting gaze stimuli or non biological directional cues (arrows) were presented to observers performing an instructed saccadic eye movement task. Eye movement recordings showed that observers performed less accurately when the distracting gaze and the instructed saccade had opposite directions, with a substantial number of saccades matching the direction of the distracting gaze. Static (Experiment 1) and dynamic (Experiment 2) gaze distracters, but not pointing arrows (Experiment 3), produced the effect. Results show a strong predisposition of humans to imitate somebody else's oculomotor behaviour, even when detrimental to task performance. This is likely linked to a strong tendency to share attentional states of other individuals, known as joint attention.

Adult↗

PubMed2002

Serial attention mechanisms in visual search: a direct behavioral demonstration.

In visual search, inefficient performance of human observers is typically characterized by a steady increase in reaction time with the number of array elements-the so-called set-size effect. In general, set-size effects are taken to indicate that processing of the array elements depends on limited-capacity resources, that is, it involves attention. Contrasting theories have been proposed to account for this attentional involvement, however. While some theories have attributed set-size effects to the intervention of serial attention mechanisms, others have explained set-size effects in terms of parallel, competitive architectures. Conclusive evidence in favor of one or the other notion is still lacking. Especially in view of the wide use of visual search paradigms to explore the functional neuroanatomy of attentional mechanisms in the primate brain, it becomes essential that the nature of the attentional involvement in these paradigms be clearly defined at the behavioral level. Here we report a series of experiments showing that highly inefficient search indeed recruits serial attention deployment to the individual array elements. In addition, we describe a number of behavioral signatures of serial attention in visual search that can be used in future investigations to attest a similar involvement of serial attention in other search paradigms. We claim that only after having recognized these signatures can one be confident that truly serial mechanisms are engaged in a given visual search task, thus making it amenable for exploring the functional neuroanatomy underlying its performance.

Adult↗