Overview (50 minute talk)

Differences in cognition and perception are thought to emerge from differences in the dynamic activity of functional brain networks. These networks exist over a broad range of spatial and temporal scales with different modalities or approaches revealing different subsets of networks. With electrophysiology (EEG) frequency tagging, oscillating visual or auditory inputs were presented and different cortical networks entrained to different input frequencies, revealing their functionally distinct properties. With event-related potentials (ERPs), evoked responses were measured and averaged over a series of discrete inputs, and the multiplexed ERP response was subsequently decomposed with multi-subject independent components analysis (ICA). I discuss this approach in the talk linked below and demonstrate relationships between ERP amplitudes and attention and cognitive control in healthy and clinical populations. The multi-subject approach also demonstrates considerable utility for resting EEG, revealing distinct spatiospectral maps which were linked with concurrent fMRI for improved spatiospectral resolution of human brain dynamics.

link to video

Perceptual representation in Schizophrenia

One of the brain’s essential functions is to integrate individuals internal goals with the external environment. In order to accomplish this goal the brain makes predictions about the environment and updates its predictions with new stimuli. This aspect of neural processing can be examined experimentally by comparing responses to expected and unexpected stimuli, as in visual or auditory oddball tasks. In addition to comparing the average response to expected and unexpected stimuli, it is also important to examine how the sequence of past events may account for fluctuations in the response to a given stimulus. These modulations would reflect an individuals attentional and perceptual sensitivity to subtle differences in the environment. Using this technique and ERP recordings, my recent research distinguishes neural responses that are modulated by sensory regularities to a greater extent in healthy individuals, than in individuals diagnosed with schizophrenia. This approach can be applied to a broad range of cognitive tasks to understand how moment by moment changes in the environment relates to moment by moment changes in attention and perception.

Figure: 2014 Bridwell Schizophrenia Research

Bridwell, D.A., Kiehl, K.A., Pearlson, G.D., Calhoun, V.D. (2014) Patients with schizophrenia demonstrate reduced cortical sensitivity to auditory oddball regularities. Schizophrenia Research, 158(1-3):189-94.

Attentional Biases: Enhancement and Suppression

Figure: 2012 Bridwell Psychological Science

The frequency-tagging technique is a powerful approach to examine how large-scale brain networks are modulated by attention. In general, my approach is to have individuals perform a task at fixation which encourages enhancing or suppressing a particular visual feature, such as horizontal orientations. Attentional gain toward features is probed my measuring steady-state visual evoked potential (SSVEP) responses to an unattended flicker containing that feature. My first findings with this technique, published in Psychological Science, demonstrate distinct cortical networks for attentional enhancement and suppression. These findings could contribute to our understanding of the attentional biases that facilitate pathologies such as addiction, and changes in attention and perception that occur as individuals age.

Bridwell, D.A., Srinivasan, R. (2012) Distinct attention networks for feature enhancement and suppression in vision. Psychological Science, 23(1):1151-1158.

Depression Symptoms and Cognitive Control

There is considerable heterogeneity among the symptoms expressed by individuals within a given clinical population. This heterogeneity is particularly prominent within depression, where two individuals can each be diagnosed with depression with non-overlapping subsets of symptoms. The heterogeneity of the population is often paralleled with heterogeneity in the research findings that emerge from the population. For example, there is remarkable inconsistency with respect to the relationship between error event-related potential (ERP) amplitudes in individuals diagnosed with depression. These inconsistencies may be better understood by focusing on depression symptoms specifically, instead of the categorical diagnosis. I advanced this possibility within a recent publication demonstrating that reductions in somatic depression symptoms were related to increased error ERP amplitudes, and that cognitive-affective symptoms were unrelated to error ERP amplitudes. In general, there is utility in understanding mental disorders from a symptom-based perceptive (as opposed to focusing on categorical diagnosis) and characterizing the relationship between individual symptom profiles and cognitive and cortical measures of attention and cognitive control.

Figure: 2014 Bridwell Affective Disorders

Bridwell, D.A., Steele, V.R., Maurer, M.J., Kiehl, K.A., Calhoun, V.D. (2015) The relationship between somatic and cognitive-affective depression symptoms and error-related ERP's. Journal of Affective Disorders, 172(1):89-95.

Individual Differences in Attention Strategies

We examined the degree to which individuals attend to visual features within and across Detection, Fine Discrimination, and Coarse Discrimination tasks. Individuals attentional tuning was measured by recording EEG responses to an unattended peripheral flickering grating while individuals attended to orientations that were offset by 0°, 10°, 20°, 30°, 40°, and 90° from the orientation of the unattended flicker. These unattended responses may be sensitive to attentional gain at the attended spatial location, since attention to features enhances early visual responses throughout the visual field. We characterized individual attention strategies using hierarchical Bayesian modeling, which grouped individuals into families of curves that reflect attention to the physical target orientation (“on-channel”) or away from the target orientation (“off-channel”) or a uniform distribution of attention. The results highlight the perceptual benefits of attending away from the physical target orientation during fine discriminations. In addition, we showed that a subset of individuals with optimal curves (“on-channel”) during Detection also demonstrated optimal curves (“off-channel”) during Fine Discrimination, indicating that a subset of individuals can modulate tuning optimally for different tasks.

Figure: 2013 Bridwell Journal of Neurophysiology

Bridwell, D.A., Hecker, E.A., Serences, J.T., Srinivasan, R. (2013) Individual differences in attention strategies during detection, fine discrimination, and coarse discrimination. Journal of Neurophysiology, 110:784-7942.