Norman Forschack | Universität Leipzig (original) (raw)

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Papers by Norman Forschack

Journal of Cognitive Neuroscience

Recent EEG studies have investigated basic principles of feature-based attention by means of freq... more Recent EEG studies have investigated basic principles of feature-based attention by means of frequency-tagged random dot kinematograms in which different colors are simultaneously presented at different temporal frequencies to elicit steady-state visual evoked potentials (SSVEPs). These experiments consistently showed global facilitation of the to-be-attended random dot kinematogram—a basic principle of feature-based attention. SSVEP source estimation suggested that posterior visual cortex from V1 to area hMT+/V5 is broadly activated by frequency-tagged stimuli. What is presently unknown is whether the feature-based attentional facilitation of SSVEPs is a rather unspecific neural response including all visual areas that follow the “on/off,” or whether SSVEP feature-based amplitude enhancements are driven by activity in visual areas most sensitive to a specific feature, such as V4v in the case of color. Here, we leverage multimodal SSVEP-fMRI recordings in human participants and a mu...

Journal of Experimental Psychology: General

Attention, Perception, & Psychophysics

This study used a typical four-item search display to investigate top-down control over attention... more This study used a typical four-item search display to investigate top-down control over attentional capture in an additional singleton paradigm. By manipulating target and distractor color and shape, stimulus saliency relative to the remaining items was systematically varied. One group of participants discriminated the side of a dot within a salient orange target (ST group) presented with green circles (fillers) and a green diamond distractor. A second group discriminated the side of the dot within a green diamond target presented with green circle fillers and a salient orange square distractor (SD group). Results showed faster reaction times and a shorter latency of the N2pc component in the event-related potential (ERP) to the more salient targets in the ST group. Both salient and less salient distractors elicited Pd components of equal amplitude. Behaviorally, no task interference was observed with the less salient distractor, indicating the prevention of attentional capture. How...

NeuroImage, Jan 31, 2018

In a recent electrophysiological study, we reported on global facilitation but local suppression ... more In a recent electrophysiological study, we reported on global facilitation but local suppression of color stimuli in feature-based attention in human early visual cortex. Subjects attended to one of two centrally located superimposed red/blue random dot kinematograms (RDKs). Task-irrelevant single RDKs in the same colors were presented in the left and right periphery, respectively. Suppression of the to-be-ignored color was only present in the centrally located RDK but not in the one with the same color in the periphery. This result was at odds with the idea of active suppression of task-irrelevant features across the entire visual field. In the present study, we introduced competition in the periphery by superimposing the RDKs at the task-irrelevant location as well. With such competition, we found suppression of the task-irrelevant color in the centrally and peripherally located RDKs. Results clearly demonstrate that suppression of task-irrelevant features at task-irrelevant locat...

Journal of cognitive neuroscience, Jan 29, 2016

A key property of feature-based attention is global facilitation of the attended feature througho... more A key property of feature-based attention is global facilitation of the attended feature throughout the visual field. Previously, we presented superimposed red and blue randomly moving dot kinematograms (RDKs) flickering at a different frequency each to elicit frequency-specific steady-state visual evoked potentials (SSVEPs) that allowed us to analyze neural dynamics in early visual cortex when participants shifted attention to one of the two colors. Results showed amplification of the attended and suppression of the unattended color as measured by SSVEP amplitudes. Here, we tested whether the suppression of the unattended color also operates globally. To this end, we presented superimposed flickering red and blue RDKs in the center of a screen and a red and blue RDK in the left and right periphery, respectively, also flickering at different frequencies. Participants shifted attention to one color of the superimposed RDKs in the center to discriminate coherent motion events in the a...

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 2015

Most sensory input to our body is not consciously perceived. Nevertheless, it may reach the corte... more Most sensory input to our body is not consciously perceived. Nevertheless, it may reach the cortex and influence our behavior. In this study, we investigated noninvasive neural signatures of unconscious cortical stimulus processing to understand mechanisms, which (1) prevent low-intensity somatosensory stimuli from getting access to conscious experience and which (2) can explain the associated impediment of conscious perception for additional stimuli. Stimulation of digit 2 in humans far below the detection threshold elicited a cortical evoked potential (P1) at 60 ms, but no further somatosensory evoked potential components. No event-related desynchronization was detected; rather, there was a transient synchronization in the alpha frequency range. Using the same stimulation during fMRI, a reduced centrality of contralateral primary somatosensory cortex (SI) was found, which appeared to be mainly driven by reduced functional connectivity to frontoparietal areas. We conclude that afte...

The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 19, 2017

Attention filters and weights sensory information according to behavioral demands. Stimulus-relat... more Attention filters and weights sensory information according to behavioral demands. Stimulus-related neural responses are increased for the attended stimulus. Does alpha-band activity mediate this effect and is it restricted to conscious sensory events (suprathreshold), or does it also extend to unconscious stimuli (subthreshold)? To address these questions, we recorded EEG in healthy male and female volunteers undergoing subthreshold and suprathreshold somatosensory electrical stimulation to the left or right index finger. The task was to detect stimulation at the randomly alternated cued index finger. Under attention, amplitudes of somatosensory evoked potentials increased 50--60 ms after stimulation (P1) for both suprathreshold and subthreshold events. Pre-stimulus amplitude of peri-Rolandic alpha, that is mu, showed an inverse relationship to P1 amplitude during attention, compared to when the finger was unattended. Interestingly, intermediate and high amplitudes of mu rhythm wer...

Cerebral Cortex

This study used electrophysiological measures to investigate how attention is deployed to target ... more This study used electrophysiological measures to investigate how attention is deployed to target and distractor stimuli during visual search using search displays with a small set-size. Participants viewed randomized sequences of two-item displays that consisted of either a target and a distractor (differing in color) or a pair of task-irrelevant filler stimuli having a third color, all presented in an ongoing stream of flickering gray circles. The allocation of attention was assessed by concurrent recordings of steady-state visual evoked potentials (SSVEPs) elicited by the flickering displays and perturbations of the endogenous alpha rhythm following each type of display. The aim was to test a central prediction of the signal suppression hypothesis, namely that the processing of distractors will be proactively suppressed below the level of filler stimuli. Amplitude modulations of both the SSVEP and the lateralized alpha rhythm provided converging evidence against early proactive su...

Scenes are so rich in information that the visual system cannot process all inputs simultaneously... more Scenes are so rich in information that the visual system cannot process all inputs simultaneously. Visual attention is the process that allows us to select the information that is relevant to our current behavior from the multiple inputs available at any given moment. Previous chapters have focused on the role of spatial and feature-based attention in selection. Here we show that attention can operate not only on the basis of locations and visual features but also by selecting an object as a whole. One way to study object-based attention is to require attention to a stimulus that is spatially superimposed on another, a situation which precludes spatial selection. Several studies have shown that it is possible to attend selectively to one of two transparent surfaces, finding that it is easier to divide attention between attributes of the same surface (e.g., direction and speed of motion) than between identical attributes for different surfaces. Moreover, attending to one feature caus...