V-VSS, June 1-2
Talk 1, 6:30 pm, 85.71
Alpha-band desynchronization predicts attractor dynamics in visual working memory
Sanchit Gupta1, Devarajan Sridharan1; 1Centre for Neuroscience, Indian Institute of Science, Bangalore
Visual working memory (WM) is known to exhibit attractor dynamics, wherein mnemonic representations drift toward discrete, stable attractor states [1,2]. Maintenance in WM is also accompanied by specific patterns of synchronization and desynchronization in parieto-occipital alpha-band (8-12 Hz) oscillations . Yet, the link between alpha desynchronization and attractor dynamics in WM remains unexplored. We tested n=24 human participants on a visual WM task involving delayed (~2500 ms) reporting of a retro-cued grating’s orientation. Although grating orientations were uniformly distributed across trials, participants’ orientation reports systematically favored the nearest diagonal orientations and were biased away from cardinal orientations, indicating stable and unstable fixed points (attractors) at these orientations, respectively. We investigated the behavioral and neural correlates of these attractor dynamics. We quantified the magnitude of bias in orientation reports (“attractor strength”) for each participant, and divided (median-split) participants into “weak” (n=12) and “strong” (n=12) attractor groups. Weak attractor participants were significantly more precise with reporting stimulus orientations, both for the WM cued (p=0.017) and uncued stimuli (p=0.030). Interestingly, weak attractor participants exhibited stronger alpha desynchronization as compared to strong attractor participants. In fact, the level of alpha desynchronization correlated robustly (and negatively) with attractor strength across individuals (p<0.05). Moreover, cue-induced alpha desynchronization -- the difference between alpha power in the parieto-occipital cortex contralateral versus ipsilateral to the WM cue -- also strongly predicted attractor strengths, across individuals (p<0.05). Contrary to recent reports , these results show that attractor dynamics do not produce an obligatory increase in working memory performance. Rather, alpha-band desynchronization may constitute a key neural mechanism governing the strength of attractor dynamics in visual WM. References: 1. Bae et-al, 2014. PMID:24715329 2. Panichello et-al, 2019. PMID:31358740 3. Wianda et-al, 2019. PMID:30887701
Talk 2, 6:45 pm, 85.72
The time course of chromatic adaptation in human early visual cortex revealed by SSVEPs
Previous studies have identified at least two components of chromatic adaptation: a rapid component within a time scale between tens of milliseconds to a few seconds, and a slow component with a half-life of about 10s-30s. The basis of the rapid adaptation probably lies in receptor adaptation at the retina. However, the neural substrate for the slow adaptation remains unclear, although previous psychophysical results hint at the early visual cortex. A promising approach to investigate adaptation effect in the visual cortex is to analyze steady-state visually evoked potentials (SSVEPs) induced by chromatic stimuli, which typically use long durations of stimulation. Here, we re-analyzed the data from two previous SSVEP studies (Chen, Valsecchi & Gegenfurtner, 2017a, 2017b). In these experiments (N = 49 observers in total), SSVEPs were induced by flickering color- or luminance-defined grating stimuli for 150 seconds in each trial. By analyzing SSVEPs with short-window frequency analysis (window size = 4 seconds), we found that chromatic SSVEP responses decreased with increasing stimulating duration and reached a lower asymptote within a minute of stimulation. In line with earlier studies, the luminance SSVEPs did not show any systematic adaptation. The time course of chromatic SSVEPs can be well described by an exponential decay function with a half-life of about 20 seconds, which is very close to previous psychophysical reports (Rinner & Gegenfurtner, 2000; Werner, Sharpe & Zrenner, 2000). This result suggests that slow-phase chromatic adaptation happens already in the early visual cortex. In addition, the current result also provides a guide for future color SSVEP studies in terms of either avoiding or exploiting the adaptation effect.
Acknowledgements: National Natural Science Foundation of China [grant number 31900758]
Talk 3, 7:00 pm, 85.73
The spatiotemporal transformation of color in the early visual cortex of humans: evidence from steady-state visual evoked potentials
The human chromatic contrast sensitivity measured with psychophysics has a lowpass shape. Human neurophysiology results, in contrast, have revealed extensively spatially-tuned bandpass population responses in the early visual cortex (e.g., Rabin, Switkes, Crognale, Schneck & Adams, 1994; Nunez, Shapley & Gordon, 2018). In monkey single-neuron studies, it has been demonstrated that there is a dynamic transformation from non-spatial tunning to spatially-tuned color responses in V1 (Johnson, Hawken & Shapley, 2001). However, such a transformation has never been identified in humans. Here, we investigated the spatial tuning of color in human observers (N = 16), by recording steady-state visual evoked potentials (SSVEPs), which originate from early visual cortex especially the V1. We tested stimuli in red-green, blue-yellow and luminance (i.e., L-M, S, and Luminance axis in DKL space), at different spatial frequencies (0.2, 1, 2, 3, 4 and 8 cycles/deg), at both low and high temporal frequency (3 Hz and 15 Hz). The results reveal a dynamic change in spatial selectivity from high to low temporal frequency: color SSVEP is low-pass at 15Hz and band-pass at 3Hz. The low-pass and band-pass color SSVEP resembles neural responses of single-opponent and double-opponent V1 neurons, respectively, in macaque monkey (Johnson, Hawken & Shapley, 2001). In addition, in the band-pass responses at 3Hz, the preferred spatial frequency for S is lower than those for L-M and luminance, which is also consistent with monkey single neuron results. SSVEP to luminance is band-pass at both 15Hz and 3Hz, suggesting that the transformation is specific to color processing. The current result reveals a spatiotemporal interaction in human color vision. The visual cortex adds spatial selectivity for color boundaries in the processing of temporal filtering.
Acknowledgements: National Natural Science Foundation of China [grant number 31900758]
Talk 4, 7:15 pm, 85.74
A trajectory aftereffect depending on the perceived trajectory of the double-drift illusion
Ryohei Nakayama1, Mai Tanaka1, Ikuya Murakami1; 1The University of Tokyo
It has been proposed that to determine the direction of object motion, the visual system can use the orientation information in motion trajectory that is available as visible persistence (Geisler, 1999). The present study dissociated the contributions of the physical and perceived trajectories by taking advantage of the double-drift illusion, in which the perceived trajectory of object motion over seconds is shifted in the direction of internal grating motion. In each trial, observers adapted for 5 s (or 35 s for the first trial in each block) to an array of Gabor patches each going up and down at 16.5 deg/s and reversing the direction every 0.5 s asynchronously to each other but synchronously with the directional reversal of its own carrier drifting horizontally at 5.5 deg/s. They appeared to be moving along tilted trajectories due to the double-drift illusion. To test a trajectory aftereffect, a luminance blob in motion at 11 deg/s was subsequently presented for 0.5 s and the subjective verticality of its trajectory was determined with the method of constant stimuli. Depending on the directional combination of the patch and carrier movements of the adaptors, and therefore depending on the direction of the double-drift illusion, the subjective verticality differed by 18.5˚ (SE = 1.0˚) when tested in the same hemifield as the adapted one and 7.1˚ (SE = 0.7˚) in the opposite hemifield. The difference was not accounted for by local motion adaptation to the internal grating motion per se because its direction was frequently reversed. This negative aftereffect also occurred to the same extent after adaptation to Gabor patches moving along physically tilted trajectories. The overall results suggest that in this instance, the perceptual, rather than physical, motion trajectories provide the spatial code for motion direction at the neural loci without hemifield specificity.
Acknowledgements: Supported by JSPS KAKENHI 21K13745 to RN and 18H05523 to IM
Talk 5, 7:30 pm, 85.75
Attention drives human numerosity selective responses
Yuxuan Cai1,2 (), Shir Hofstetter1, Ben Harvey3, Serge Dumoulin1,2,3,4; 1Spinoza Centre for Neuroimaging, Amsterdam, Netherlands, 2VU University Amsterdam, Amsterdam, Netherlands, 3Utrecht University, Utrecht, Netherlands, 4Netherlands Institude for Neuroscience
Introduction Numerosity, the set size of a group of items, helps guide behaviour and decisions. Previous studies have shown that neural populations respond selectively to numerosities. How numerosity is extracted from the visual scene is a longstanding debate, often contrasting low-level visual with high-level cognitive processes. Here, using 7T functional MRI, we investigate how attention influences numerosity selective responses. Method 4 participants took part in three experiments. In all experiments, the stimuli consisted of black and white dots within the same display, and the participants’ attention was focused on either black or white dots while detecting a subtle shape change of the attended dot subset. In Experiment1, the white dots systematically increased from 1 to 7, while the black dots systematically decreased from 26 to 20, keeping the total numerosity constant at 27. Here, we summarized the fMRI signals responding to the attended dot subset’s numerosity using population receptive field modelling (Dumoulin & Wandell, 2008). In experiments2, we used a 2x2 block design to establish the response to the preferred, but unattended numerosities. The subset consisting of 2/3/4 (the preferred numerosities) dots were presented while being attended and unattended, respectively. The total numerosity was fixed at 40 with the non-preferred numerosities varied from 36-38. In Experiment 3 only one non-preferred numerosity of 20 dots was shown, and as a result, the total numerosity varied. The neural responses in experiments 2-3 were analysed using general linear models. Results We found that the numerosity-tuned neural populations respond only when attention is focused on their preferred numerosity, irrespective of the unattended or total numerosities. Without attention, responses to preferred numerosity were inhibited. Conclusions Unlike traditional effects of attention in the visual cortex where attention enhances already existing responses, our results suggest that attention is required to drive numerosity selective responses.
Acknowledgements: This research was supported by a China Scholarship Council (CSC) scholarship  (Y. C.), an NWO-VICI grant 016.Vici.185.050 (S. O. D.) and an NWO-VIDI grant 452-117-012 (B. M. H.).
Talk 6, 7:45 pm, 85.76
Effects of unconscious action learning on action and perception
Jie Gao1 (), Zhiqing Deng1, Yichong Zhang1, Juan Chen1,2; 1Center for the Study of Applied Psychology, Guangdong Key Laboratory of Mental Health and Cognitive Science, and the School of Psychology, South China Normal University, Guangzhou, Guangdong Province, 510631, China, 2Key Laboratory of Brain, Cognition and Education Sciences (South China Normal University), Ministry of Education
Perception learning is a way to improve people’s sensory ability by extensive training. Researchers have been investigating the specificity of perceptual learning and the extent to which it can be transferred to untrained features or locations for decades. It is still unclear whether or not learning can transfer across the two visual pathways: the ventral pathway mediating visual perception and the dorsal pathway mediating visuomotor skills. If action learning could transfer to visual perception or vice versa, then we can use this transfer to design training protocols to help patients with either ventral or dorsal lesions. Given that patients with ventral lesions usually have deficits in visual perception, to mimic the situation of this kind of patient, we made stimuli (a long and narrow rectangle frame, either horizontal or vertical) invisible with continuous flash suppression (CFS) and trained participants to pretend to insert a card into the frame (action learning). Participants were tested before, four days after, or eight days after training. There were three kinds of tests, a sensitivity test which tests the contrast at which the orientation of the frame could be recognized at 75% accuracy, an action test in which participants were asked to post the card into the frame, and a perception test in which participants were asked to verbally report the orientation of the frame. We found that after eight days of training, participants’ performance in all three tasks was improved. The amount of action and perception improvement was correlated with each other. The amount of perception improvement after action learning was correlated with the depth of unconsciousness (i.e., the ratio of stimulus contrast to the contrast threshold of each participant before training). Overall, our study suggests that the learning effect can transfer across the two pathways.
Acknowledgements: This study was supported by two grants from the National Natural Science Foundation of China (31800908 and 31970981).