Biomedical subjects

Anthony Singhal

Publications and source records attributed to Anthony Singhal.

7 recordsLinked to original sources

PubMed2006

Differentiating between spatial and object-based working memory using complex stimuli: an erp study.

Event-related potential studies using simple low-level stimuli have associated early visual-spatial processing with P1 amplitude, and early visual object-based processing with N2 amplitude. Other studies have linked later spatial processing and spatial working memory with posterior slow wave activity. Using complex real world representations in a matched object and spatial processing task, P1 was found to reflect spatially based information, and N2 was found to reflect object-based information. Furthermore, object-based working memory was associated with larger slow wave amplitude compared with spatial working memory, raising the possibility that spatial and object-based working memory utilize common processing resources.

Adult↗

PubMed2005

The role of parietal cortex in visuomotor control: what have we learned from neuroimaging?

Research from macaque neurophysiology and human neuropsychology has implicated the parietal cortex in the sensory control of action. Functional neuroimaging has been very valuable in localizing and characterizing specific regions of the human brain involved in visuomotor actions involving different effectors, such as the eyes, head, arms and hands. Here, we review the areas discovered by human neuroimaging, including the putative functional equivalents of the following macaque regions: parietal eye fields (PEF), ventral intraparietal (VIP) area, parietal reach region (PRR) and the anterior intraparietal (AIP) area. We discuss the challenges of studying realistic movements in the imaging environment, the lateralization of visuomotor function, caveats involved in proposing interspecies homologies and the limitations and future directions for neuroimaging studies of visuomotor control.

Animals↗

PubMed2005

Influence of a visual spatial attention task on auditory early and late Nd and P300.

Singhal et al. [Psychophysiology 39 (2002) 236] reported that the amplitude of the late negative difference (Nd) and P300 components, generated by a dichotic listening task, were decreased in parallel by a simultaneously performed visual flying task. In contrast, early Nd was unaffected. To investigate the role of covert spatial attention in this pattern of results, we substituted Posner's attention switching paradigm for the flying task. Fourteen subjects performed the dichotic listening and attention tasks alone and in combination. The results showed that only the invalid/valid condition of the Posner task reduced the amplitude of the late Nd, while the early Nd was unaffected. Contrary to the earlier study, P300 dissociated from the late Nd and its amplitude decreased in both the invalid/valid and neutral conditions of the Posner task. We conclude that the late Nd is sensitive to some aspect of attention switching and that the late Nd and P300 share sensitivity to an amodal system to which the early Nd is insensitive. Within this system, the late Nd is differentiated from P300 by its narrow sensitivity to attentional processing whereas P300 is sensitive to a broader range of processing. These similarities and differences are explained in the context of a modified version of Kok's model [Psychophysiology 38 (2001) 557] of the determinants of P300 amplitude.

Adult↗

PubMed2005

The effects of memory scanning on the late Nd and P300: an interference study.

Singhal and Fowler (2004) showed that the late negative difference (Nd) waveform elicited during dichotic listening was attenuated by concurrent visual short term memory (STM) scanning, but not long term memory (LTM) scanning. P300 was reduced by both tasks. The present study compared the effects of STM load on the late Nd and P300 by combining dichotic listening and visual memory scanning with varying set sizes. The results showed that the late Nd was sensitive to the introduction of the scanning task, but not to an increase in load. Furthermore, both the auditory and visual P300s were reduced when a second task was introduced, but only the visual P300 decreased as a function of memory-set size. These data suggest that (a) the auditory late Nd reflects working memory, but not memory scanning, (b) late Nd and P300 reflect parallel but distinct working memory processes, and (c) stimulus modality is an important determinant of P300 amplitude.

Adult↗

PubMed2005

The late Nd reflects a memory trace containing amodal spatial information.

The early Nd reflects the analysis of simple features of selectively attended auditory stimuli, but the precise nature of the more complex processing reflected by the late Nd is unclear. The late but not the early Nd is sensitive to interference from a concurrently presented visual spatial attention switching task. This experiment investigated whether the late Nd is also sensitive to deeper visual attention switching. Twenty-one subjects performed a dichotic listening task concurrently with either visual spatial or visual letter matching attention switching tasks. Late Nd amplitude was reduced by the spatial but not the letter matching task, indicating insensitivity to deeper attention switching. P300 amplitude was reduced by both tasks. Reductions in N100 and P200 were uncorrelated. We propose that, in part, the late Nd reflects an amodal memory trace containing spatial information, possibly involving a "where" rather than a "what" auditory pathway.

Adolescent↗

PubMed2004

The differential effects of Sternberg short- and long-term memory scanning on the late Nd and P300 in a dual-task paradigm.

We previously reported that the late negative difference (Nd) waveform elicited during dichotic listening was reduced in amplitude by a concurrent simulated flying task having a wide variety of cognitive demands (Psychophysiology, 39, 2002, 236). The main purpose of the present study was to determine how tasks involving the specific demands of short-term memory (STM) or long-term memory (LTM) would influence the early and late Nd waveforms. To this end, 16 participants performed dichotic listening alone and in conjunction with the varied-set (STM) and fixed-set (LTM) versions of Sternberg's memory scanning paradigm. Event-related brain potential (ERP) data was collected concurrently from both the auditory and visual tasks. The results showed that the STM task, but not the LTM task, reduced the amplitude of the auditory late Nd. The auditory early Nd component was unaffected by either task. Furthermore, both the auditory and visual P300s were decreased in amplitude by all the dual-task conditions. These data suggest that the auditory late Nd is linked to more specific working memory processes than is P300.

Acoustic Stimulation↗

PubMed2002

Effects of a dual task on the N100-P200 complex and the early and late Nd attention waveforms.

The roles of N100 and the early and late negative difference (Nd) waveforms in selective attention were investigated with primary simulated flying and secondary dichotic listening tasks. Twenty highly trained participants performed the two tasks together, either while detecting secondary task deviant tones in one ear and ignoring tones in the other ear (dual condition) or while ignoring the tones in both ears (ignore condition). The amplitude of the N100-P200 complex in both the dual-task and ignore conditions was reduced equally in the attended and unattended ear by the introduction of the primary task. In the dual-task condition, the amplitude of the late Nd but not the early Nd was reduced by a combination of the introduction of the primary task and an increase in its difficulty. P300 showed the same amplitude pattern as the late Nd. We propose that the reduction in N100-P200 amplitude reflects an automatic gating mechanism. The dissociation of the early and late Nd suggests that the latter is not modality specific. The question is raised whether the late Nd is more closely associated with P300 than with the early Nd.

Adolescent↗