Biomedical subjects

P Pazo-Alvarez

Publications and source records attributed to P Pazo-Alvarez.

3 recordsLinked to original sources

PubMed2006

Functional neuroimaging with MEG: normative language profiles.

The reliability of language-specific brain activation profiles was assessed using Magnetoencephalography (MEG) in five experiments involving ninety-seven normal volunteers of both genders ranging in age from seven to eighty-four years. MEG data were analyzed with a fully automated method to eliminate subjective judgments in the process of deriving the activation profiles. Across all experiments, profiles were characterized by significant bilateral activity centered in the superior temporal gyrus, and in activity lateralized to the left middle temporal gyrus. These features were invariant across age, gender, variation in task characteristics, and mode of stimulus presentation. The absolute amount of activation, however, did decline with age in the auditory tasks. Moreover, contrary to the commonly held belief that left hemisphere dominance for language is greater in men than in women, our data revealed an opposite albeit a not consistently significant trend.

Adolescent↗

PubMed2004

Automatic detection of motion direction changes in the human brain.

The possibility that the visual system is able to register unattended changes is still debated in the literature. However, it is difficult to understand how a sensory system becomes aware of unexpected salient changes in the environment if attention is required for detecting them. The ability to automatically detect unusual changes in the sensory environment is an adaptive function which has been confirmed in other sensory modalities (i.e. audition). This deviance detector mechanism has proven to be based on a preattentive nonrefractory memory-comparison process. To investigate whether such automatic change detection mechanism exists in the human visual system, we recorded event-related potentials to sudden changes in a biologically important feature, motion direction. Unattended sinusoidal gratings varying in motion direction in the peripheral field were presented while subjects performed a central task with two levels of difficulty. We found a larger negative displacement in the electrophysiological response elicited by less frequent stimuli (deviant) at posterior scalp locations. Within the latency range of the visual evoked component N2, this differential response was elicited independently of the direction of motion and processing load. Moreover, the results showed that the negativity elicited by deviants was not related to a differential refractory state between the electrophysiological responses to frequent and infrequent directions of motion, and that it was restricted to scalp locations related to motion processing areas. The present results suggest that a change-detection mechanism sensitive to unattended changes in motion direction may exist in the human visual system.

Adult↗

PubMed2003

MMN in the visual modality: a review.

The mismatch negativity (MMN) component is an event-related potential (ERP) that can be elicited by any change in the acoustic environment, and it is related to memory-based, automatic processing mechanisms, and attentional capture processes. This component is well defined in the auditory modality. However, there is still a great controversy about its existence in the visual modality. This paper reviews the studies that are relevant with regard to memory-based, automatic deviance detection ERPs in the visual system. The paper discusses the main strengths and limitations of those studies and suggests what directions should be taken for future research.

Attention↗