Biology subjects

Nadra, J. G.

Publications and source records attributed to Nadra, J. G..

3 recordsLinked to original sources

bioRxiv2025

Volitional Attention to Color: Breaking Willed Attention out of the Spatial Domain

Attention can be guided by either voluntary (top-down) or involuntary (bottom-up) influences. In real-world vision, voluntary attention can be directed by a wide range of influences such as reward, priming, meaning, experience, selection history, and volition. Laboratory studies of voluntary attention have commonly used attention-directing cues to induce or instruct human subjects to attend one class of stimuli while ignoring others. In recent years, free choice conditions of attention have been introduced, where self-generated volitional shifts of attention (willed attention) are possible (for a review, see Nadra & Mangun, 2023). Prior willed attention studies have focused on mechanisms of covert spatial attention, investigating the neurophysiological correlates of willed attention related to both post-decision processing, and the pre-decision brain activity patterns that predict participants free choices about where to attend. Much less work, however, has been done on willed non-spatial attention. In this study, in a fashion similar to prior willed spatial attention studies, we investigated willed attention to stimulus color. In a trial-by-trial cueing design, subjects were either cued what color to attend or were allowed to freely choose what color to attend, in order to subsequently discriminate visual features of the cued or willfully chosen target. Behavioral measures showed that the subjects were selectively attending the cued or willed color. Using support vector machine decoding on EEG alpha (8-12 Hz) signals, we found significant post-decision differences in alpha-band power and broadband EEG voltage when participants chose to attend to orange versus purple. However, in contrast to the findings in prior work on willed spatial attention, no pre-decision EEG signals could be identified that predicted which color participants would choose to attend to.

neuroscience↗

bioRxiv2025

Unconscious Neural Activity Predicts Overt Attention in Visual Search

Unconscious neural activity has been shown to precede both motor and cognitive acts. In the present study, we investigated the neural antecedents of overt attention during visual search, where subjects make voluntary saccadic eye movements to search a cluttered stimulus array for a target item. Building on studies of both overt self-generated motor actions (Lau et al., 2004, Soon et al., 2008) and self-generated cognitive actions (Bengson et al., 2014, Soon et al., 2013), we hypothesized that brain activity prior to the onset of a search array would predict the direction of the first saccade during unguided visual search. Because both spatial attention and gaze are coordinated during visual search, both cognition and motor actions are coupled during visual search. A well-established finding in fMRI studies of willed action is that neural antecedents of the intention to make a motor act (e.g., reaching) can be identified seconds before the action occurs. Studies of the volitional control of covert spatial attention in EEG have shown that predictive brain activity is limited to only a few hundred milliseconds before a voluntary shift of covert spatial attention. In the present study, the visual search task and stimuli were designed so that subjects could not predict the onset of the search array. Perceptual task difficulty was high, such that they could not locate the target using covert attention alone, thus requiring overt shifts of attention (saccades) to carry out the visual search. If the first saccade to the array onset in unguided visual search shares mechanisms with willed shifts of covert attention, we expected predictive EEG alpha-band activity (8-12 Hz) immediately prior to the array onset (within 1 sec) (Bengson et al., 2014; Nadra et al., 2023). Alternatively, if they follow the principles of willed motor actions, predictive neural signals should be reflected in broadband EEG activity (Libet et al., 1983) and would likely emerge earlier (Soon et al., 2008). Applying support vector machine decoding, we found that the direction of the first saccade in an unguided visual search could be predicted up to two seconds preceding the search arrays onset in the broadband but not alpha-band EEG. These findings suggest that self-directed eye movements in visual search emerge from early preparatory neural activity more akin to willed motor actions than to covert willed attention. This highlights a distinct role for unconscious neural dynamics in shaping visual search behavior.

neuroscience↗

bioRxiv2022

The Temporal Dynamics of Willed Attention in Vision

Most models of attention distinguish between voluntary and involuntary attention, the latter being driven in a bottom-up fashion by salient sensory signals. Studies of voluntary visual-spatial attention have used informational or instructional cues, such as arrows, to induce or instruct observers to direct selective attention to relevant locations in visual space in order to detect or discriminate subsequent target stimuli. In everyday vision, however, voluntary attention is influenced by a host of factors, most of which are quite different from the laboratory paradigms that utilize attention-directing cues. These factors include priming, experience, reward, meaning, motivations, and high-level behavioral goals. Attention that is endogenously directed in the absence of external cues has been referred to as self-initiated attention, or in our prior work as "willed attention". Such studies typically replace attention-directing cues with a "prompt" that signals the subject when to choose where they will attend in preparation for the upcoming target stimulus. We used a novel paradigm that was designed to minimize external influences (i.e., cues or prompts) as to where, as well as when, spatial attention would be shifted and focused. Participants were asked to view bilateral dynamic dot motion displays, and to shift their covert spatial attention to either the left or right visual field patch at a time of their own choosing, thus allowing the participants to control both when and where they attended on each trial. The task was to discriminate and respond to a pattern in the attended dot motion patch. Our goal was to identify patterns of neural activity in the scalp-recorded EEG that revealed when and where attention was focused. Using machine learning methods to decode attention-related EEG alpha band activity, we were able to identify the onset of voluntary (willed) shifts of visual-spatial attention, and to determine where attention was focused. This work contributes to our understanding of the neural antecedents of voluntary attention, opening the door for improved models of attentional control, and providing steps toward development of brain-computer interfaces using non-invasive electrical recordings of brain activity.

neuroscience↗