Biology subjects

Gladhill, K. A.

Publications and source records attributed to Gladhill, K. A..

3 recordsLinked to original sources

bioRxiv2022

Anchors for Time, Distance, and Magnitude in Virtual Movements

In order to navigate through the environment, humans must be able to measure both the distance traveled in space, and the interval covered in time. Yet, how these two dimensions are computed and interact across neural systems remains unknown. One possibility is that subjects measure how far and how long they have traveled relative to a known reference point, or anchor. To measure this, we had human participants (n=24) perform a distance estimation task in a virtual environment in which they were cued to attend to either the spatial or temporal interval traveled, while responses were measured with multiband fMRI. We observed that both dimensions evoked similar frontoparietal networks, yet with a striking rostrocaudal dissociation between temporal and spatial estimation. Multivariate classifiers trained on each dimension were further able to predict the temporal or spatial interval traveled, with centers of activation within the supplementary motor area (SMA) and retrosplenial cortex (RSC) for time and space, respectively. Further, a cross-classification approach revealed the right supramarginal gyrus (SMG) and occipital place area (OPA) as regions capable of decoding the general magnitude of the traveled distance. Altogether, our findings suggest the brain uses separate systems for tracking spatial and temporal distances, which are combined together along with amodal estimates.

neuroscience↗

bioRxiv2020

Modulation of Individual Alpha Frequency with tACS shifts Time Perception

Previous studies have linked brain oscillation and timing, with evidence suggesting that alpha oscillations (10Hz) may serve as a "sample rate" for the visual system. However, direct manipulation of alpha oscillations and time perception has not yet been demonstrated. Eighteen subjects performed a time generalization task with visual stimuli. Participants first learned the standard intervals (600 ms) and then were required to judge the new temporal intervals if they were equal or different compared to the standard. Additionally, we had previously recorded resting-state EEG from each subject and calculated their Individual Alpha Frequency (IAF), estimated as the peak frequency from the mean spectrum over posterior electrodes between 8 and 13 Hz. After learning the standard interval, participants performed the time generalization task while receiving occipital transcranial Alternating Current Stimulation (tACS). Crucially, for each subject, tACS was administered at their IAF or at off-peak alpha frequencies (IAF{+/-}2 Hz). Results demonstrated a linear shift in the psychometric function indicating a modification of perceived duration, such that progressively "faster" alpha stimulation led to longer perceived intervals. These results provide the first evidence that direct manipulations of alpha oscillations can shift perceived time in a manner consistent with a clock speed effect.

neuroscience↗

bioRxiv2020

Dissociable Effects of Emotional Stimuli on Perception and Decision-Making for Time

Previous research has demonstrated that negative emotional faces dilate time perception, however, the mechanisms underlying this phenomenon are not fully understood. Previous attempts focus on the pacemaker-accumulator model of time perception, which includes a clock, memory, and decision-making stage, wherein emotion affects one of these stages; possibly by increasing pacemaker rate via arousal, increasing accumulation rate via attention, or by biasing decision-making. To further investigate the stage(s) that emotion is affecting time perception we conducted a visual temporal bisection task with sub-second intervals while recording 64-channel electroencephalogram (EEG). To separate the influence of face and timing responses the temporal stimulus was preceded and followed by a face stimulus displaying a neutral or negative expression creating three trial-types: Neg[->]Neut, Neut[->]Neg, or Neut[->]Neut. The data revealed a leftward shift in bisection point (BP) in Neg[->]Neut and Neut[->]Neg suggesting an overestimation of time. Neurally, we found the face-responsive N170 component was larger for negative faces and the N1 and contingent negative variation (CNV) were larger when preceded by a negative face. We also found an interaction effect between condition and response for the late positive component of timing (LPCt) and a significant difference between response (short/long) in the neutral condition. We conclude that a preceding negative face affects the clock stage leading to more pulses being accumulated, either through attention or arousal, as indexed by a larger N1, CNV, and N170; whereas viewing the negative face second biased decision-making leading to "short" responses being less likely, as evidenced by the LPCt.

neuroscience↗