Tom Bullock

Acute exercise and aerobic fitness influence selective attention during visual search

Successful goal directed behavior relies on a human attention system that is flexible and able to adapt to different conditions of physiological stress. However, the effects of physical activity on multiple aspects of selective attention and whether these effects are mediated by aerobic capacity, remains unclear. The aim of the present study was to investigate the effects of a prolonged bout of physical activity on visual search performance and perceptual distraction. Two groups of participants completed a hybrid visual search flanker/response competition task in an initial baseline session and then at 17-min intervals over a 2 h 16 min test period. Participants assigned to the exercise group engaged in steady-state aerobic exercise between completing blocks of the visual task, whereas participants assigned to the control group rested in between blocks. The key result was a correlation between individual differences in aerobic capacity and visual search performance, such that those individuals that were more fit performed the search task more quickly. Critically, this relationship only emerged in the exercise group after the physical activity had begun. The relationship was not present in either group at baseline and never emerged in the control group during the test period, suggesting that under these task demands, aerobic capacity may be an important determinant of visual search performance under physical stress. The results enhance current understanding about the relationship between exercise and cognition, and also inform current models of selective attention.

Multiple stages of information processing are modulated during acute bouts of exercise

Acute bouts of aerobic physical exercise can modulate subsequent cognitive task performance and oscillatory brain activity measured with electroencephalography (EEG). Here, we investigated the sequencing of these modulations of perceptual and cognitive processes using scalp recorded EEG acquired during exercise. Twelve participants viewed pseudo-random sequences of frequent non-target stimuli (cars), infrequent distractors (obliquely oriented faces) and infrequent targets that required a simple detection response (obliquely oriented faces, where the angle was different than the infrequent distractors). The sequences were presented while seated on a stationary bike under three conditions during which scalp recorded EEG was also acquired: rest, low-intensity exercise, and high-intensity exercise. Behavioral target detection was faster during high-intensity exercise compared to both rest and low-intensity exercise. An event-related potential (ERP) analysis of the EEG data revealed that the mean amplitude of the visual P1 component evoked by frequent non-targets measured at parietal-occipital electrodes was larger during low-intensity exercise compared to rest. The P1 component evoked by infrequent targets also peaked earlier during low-intensity exercise compared to rest and high-intensity exercise. The P3a ERP component evoked by infrequent distractors measured at parietal electrodes peaked significantly earlier during both low- and high-intensity exercise when compared to rest. The modulation of the visual P1 and the later P3a components is consistent with the conclusion that exercise modulates multiple stages of neural information processing, ranging from early stage sensory processing (P1) to post-perceptual target categorization (P3a).

Acute exercise modulates feature-selective responses in human cortex

An organisms current behavioral state influences ongoing brain activity. Nonhuman mammalian and invertebrate brains exhibit large increases in the gain of feature-selective neural responses in sensory cortex during locomotion, suggesting that the visual system becomes more sensitive when actively exploring the environment. This raises the possibility that human vision is also more sensitive during active movement. To investigate this possibility, we used an inverted encoding model technique to estimate feature-selective neural response profiles from EEG data acquired from participants performing an orientation discrimination task. Participants (n = 18) fixated at the center of a flickering (15 Hz) circular grating presented at one of nine different orientations and monitored for a brief shift in orientation that occurred on every trial. Participants completed the task while seated on a stationary exercise bike at rest and during low- and high-intensity cycling. We found evidence for inverted-U effects; such that the peak of the reconstructed feature-selective tuning profiles was highest during low-intensity exercise compared with those estimated during rest and high-intensity exercise. When modeled, these effects were driven by changes in the gain of the tuning curve and in the profile bandwidth during low-intensity exercise relative to rest. Thus, despite profound differences in visual pathways across species, these data show that sensitivity in human visual cortex is also enhanced during locomotive behavior. Our results reveal the nature of exercise-induced gain on feature-selective coding in human sensory cortex and provide valuable evidence linking the neural mechanisms of behavior state across species.

Dual process coding of recalled location in human oscillatory brain activity

A mental representation of the location of an object can be constructed using sensory information selected from the environment and information stored internally. Human electrophysiological evidence indicates that behaviorally relevant locations, regardless of the source of sensory information, are represented in alpha-band oscillations suggesting a shared process. Here we present evidence from human subjects of either sex for two distinct alpha-band based processes that separately support the representation of location, exploiting sensory evidence sampled either externally or internally. Significance Statement Our sensory environment and our internal trains of thought are coded in patterns of brain activity and are used to guide coherent behavior. Oscillations in the alpha frequency band are a predominant feature of human brain activity. This oscillation plays a central role in both selective attention and working memory, suggesting that these important cognitive functions are mediated by a unitary mechanism. We show that the alpha oscillation reflects two distinct processes, one that is supported by continuous sampling of the external sensory environment, and one that is based on sampling from internal representations coded in visual short-term memory. This represents a significant change in our understanding of the nature of alpha oscillations and their relationship to attention and memory.

Acute aerobic exercise modulates feature selectivity in human visual cortex.

Multiple cognitive functions can be modulated by acute bouts of aerobic physical exercise (Chang et al. 2012). Behavioral changes during exercise are likely accompanied by fluctuations in patterns of neural activity, but a comprehensive understanding of these effects remains elusive. For example, it is unclear whether exercise induced changes in cognition reflect non-specific effects on task performance, or whether they are specific to the task that is being performed while engaged in physical activity. We investigated this issue by testing whether acute exercise causes an additive, non-specific shift in feature-based attentional selectivity, or if it causes a multiplicative gain in selectivity. We used electroencephalography (EEG, 64 electrodes) and a gaze-contingent task that enabled orientation-selective profiles to be estimated from steady-state evoked potential (SSVEP) responses (Garcia, Srinivasan & Serences, 2013). For each trial, participants (n=3) fixated at the center of a flickering (15 Hz) circular grating presented at one of nine different orientations and monitored for a brief duration clockwise or counter-clockwise shift, and then indicated the direction of the shift at the end of the trial. Participants completed the task at rest while seated on a stationary exercise bike (mean heart rate (HR) = 68 BPM), during low intensity cycling exercise (mean HR = 103.3 BPM, mean rating of perceived exertion (RPE) = 8) and during high intensity cycling exercise (mean HR = 151.7, mean RPE = 13). The feature-selective response functions estimated from the EEG data revealed enhanced peak amplitude during low intensity (mean = .41 μV, SEM = .04 μV), and high intensity exercise (mean = .42, SEM = .05 μV) when compared to rest (mean = .29 μV, SEM = .04 μV). These findings suggest that acute bouts of aerobic exercise modulate visual cortical responses and that these modulations can be manifested as a multiplicative gain on estimated feature-selective response profiles. Meeting abstract presented at VSS 2015.