Biomedical subjects

Niko A Busch

Publications and source records attributed to Niko A Busch.

5 recordsLinked to original sources

PubMed2005

Time-frequency analysis of target detection reveals an early interface between bottom-up and top-down processes in the gamma-band.

The early visual gamma-band response is an oscillatory signal evoked approximately 100 ms after stimulation. While some studies have found effects of various cognitive processes on this signal, such effects could not be replicated in other studies. Accordingly, some authors have claimed that evoked gamma-band activity reflects merely sensory functions. To resolve these conflicting positions, we conducted a target detection experiment in which the feature that defined the target could be distributed over a large or a small part of the entire stimulus. Only targets covering a larger area of the entire stimulus evoked stronger gamma-band activity than standards although the over-all stimulus size was identical for all stimuli. This increase in evoked activity resulted from stronger oscillatory power and not exclusively from stronger phase-locking. In contrast, N1 and P3 amplitudes were larger for target stimuli irrespective of the distribution of the relevant stimulus feature. These results are consistent with the notion that early gamma-band activity is generated by feature-selective neural assemblies the activity of which can in fact be modulated by top-down processes. This interaction, however, may be only detectable in scalp-recorded EEG if it affects a sufficient number of neural assemblies.

Adult↗

PubMed2005

Circles are different: the perception of Glass patterns modulates early event-related potentials.

Glass patterns are randomized dot arrays that generate the perception of a global structure. They consist of correlated dot pairs which are generated by geometric transformations. The present study employed behavioral and event-related brain potential (ERP) measures to characterize the underlying neuronal processing when such patterns are perceived. Stimuli were circular, parallel, and randomized Glass patterns presented in two isoluminant colors using a choice reaction paradigm. Sixteen subjects were instructed to differentiate between colors with a button-press response. The N170 component increased in amplitude for circular patterns, and this effect was most pronounced bilaterally over occipito-temporal areas. The results suggest that the global perception of form generated by Glass patterns occurs at a stage of visual processing past area V1.

Adult↗

PubMed2004

Memory-matches evoke human gamma-responses.

BACKGROUND: Human brain activity in the gamma frequency range has been shown to be a correlate of numerous cognitive functions like attention, perception and memory access. More specifically, gamma activity has been found to be enhanced when stimuli are stored in or match with short-term memory (STM). We tested the hypothesis that gamma activity is also evoked when stimuli match representations in long-term-memory (LTM). EEG was recorded from 13 subjects performing a choice reaction task. Visual stimuli were either known real-world objects with a memory representation or novel configurations never seen before. RESULTS: All stimuli evoked an early gamma response which was maximal over occipital electrodes. This evoked gamma activity was significantly larger for items that matched memory templates. CONCLUSIONS: Therefore, we argue that gamma activity results from the feedback from memory into perception systems. This assumption seems to be true for STM as well as LTM.

Adult↗

PubMed2004

Size matters: effects of stimulus size, duration and eccentricity on the visual gamma-band response.

OBJECTIVE: The effects of stimulus size, duration and eccentricity on the visual gamma-band response (GBR) in human EEG were investigated and compared to visual evoked potentials (VEPs) in order to differentiate in future (and past) experiments whether changes in GBRs are due to stimulus-related (exogenous) or cognitive effects. METHODS: EEG was recorded from 23 subjects while they performed a simple choice reaction time task requiring discrimination of squares and circles. In separate blocks stimulus size, duration, and eccentricity were manipulated. EEG was recorded from 64 electrodes. A wavelet transform based on Morlet wavelets was employed for the analysis of gamma-band activity. RESULTS: Amplitude of the GBR was diminished for small and peripheral stimuli. With short stimulus durations ON and OFF responses of the GBR merged into one peak. In comparison, VEP amplitudes were less susceptible to stimulus features. In contrast to VEP latencies, however, GBR latency did not show a lateralization for eccentric stimuli. CONCLUSIONS: In addition to previous experiments which have shown a modulation of the GBR by various cognitive processes, the present results demonstrate the susceptibility of the GBR in human EEG to exogenous factors, as numerous intracortical recordings in non-human primates have shown before. The results suggest that the human GBR resides in early visual areas. SIGNIFICANCE: The demonstration of the susceptibility of the GBR to stimulus properties implies that studies aimed at exploring the involvement of the GBR in information processing have to be designed carefully. It also constrains the localization of the human GBR.

Adult↗

PubMed2003

Object-load and feature-load modulate EEG in a short-term memory task.

Behavioral studies have indicated that multiple features of one object can be stored in working memory without additional costs. In contrast, visual search experiments revealed that search for a multi-featured object takes more time than for a single-featured object. We used EEG to differentiate the effect of object-load and feature-load in a short-term memory task. We independently varied the amount of objects and features that had to be memorized. Object-load modulated P3 amplitude during encoding and induced 10 Hz oscillations during the retention interval. Feature-load modulated the P3 during retrieval. Thus, only object-load seemed to influence encoding and retention while feature-load played a crucial role during retrieval. Our results demonstrate that object-load and feature-load influence short-term memory at different stages.

Adult↗