Stimulus duration has little effect on auditory, visual and audiovisual temporal order judgement

Some classical studies on temporal order judgments (TOJ) suggested a single central process comparing stimulus onsets across modalities. The prevalent current view suggests that there is modality-specific timing estimation followed by a cross-modal stage. If the latter view is correct, TOJ's may vary depending on stimulus modality. Further, if TOJ is based only on onsets, stimulus duration should be irrelevant. To address these issues, we used both unisensory and multisensory stimuli to test whether unisensory duration processing influences cross-modal TOJ's. The stimuli were auditory noise bursts, visual squares, and their cross-modal combinations presented at 10, 40 and 500 ms durations, and various stimulus onset asynchronies. Psychometric functions were measured with an identical task in all conditions: On each trial, two stimuli were presented, one to the left, the other to the right of fixation. The participants judged which one started first. TOJ's were little affected by stimulus duration, implying that they are mainly determined by stimulus onsets. Throughout, the cross-modal just noticeable differences were larger than the unisensory ones. In accordance with the current view, our results suggest that cross-modal TOJ's require a comparison of timing after modality-specific estimations.Peer reviewe

Brightness and transparency in the early visual cortex

Peer reviewe

Radial Frequency Analysis of Contour Shapes in the Visual Cortex

Cumulative psychophysical evidence suggests that the shape of closed contours is analysed by means of their radial frequency components (RFC). However, neurophysiological evidence for RFC-based representations is still missing. We investigated the representation of radial frequency in the human visual cortex with functional magnetic resonance imaging. We parametrically varied the radial frequency, amplitude and local curvature of contour shapes. The stimuli evoked clear responses across visual areas in the univariate analysis, but the response magnitude did not depend on radial frequency or local curvature. Searchlight-based, multivariate representational similarity analysis revealed RFC specific response patterns in areas V2d, V3d, V3AB, and IPS0. Interestingly, RFC-specific representations were not found in hV4 or LO, traditionally associated with visual shape analysis. The modulation amplitude of the shapes did not affect the responses in any visual area. Local curvature, SF-spectrum and contrast energy related representations were found across visual areas but without similar specificity for visual area that was found for RFC. The results suggest that the radial frequency of a closed contour is one of the cortical shape analysis dimensions, represented in the early and mid-level visual areas.Peer reviewe

Visual working memory for amplitude-modulated shapes

Peer reviewe

Associations of subjective and objective cognitive functioning after COVID-19 : A six-month follow-up of ICU, ward, and home-isolated patients

Publisher Copyright: © 2023 The AuthorsBackground: Subjective and objective cognitive dysfunction are reported after COVID-19 but with limited data on their congruence and associations with the severity of the acute disease. The aim of this cohort study is to describe the prevalence of subjective and objective cognitive dysfunction at three and six months after COVID-19 and the associations of subjective cognitive symptoms and psychological and disease-related factors. Methods: We assessed a cohort of 184 patients at three and six months after COVID-19: 82 patients admitted to the Intensive Care Unit (ICU), 53 admitted to regular hospital wards, and 49 isolated at home. A non-COVID control group of 53 individuals was included. Demographic and clinical data were collected. Subjective cognitive symptoms, objective cognitive impairment, and depressive and post-traumatic stress disorder (PTSD) symptoms were assessed. Results: At six months, subjective cognitive impairment was reported by 32.3% of ICU-treated, 37.3% of ward-treated, and 33.3% of home-isolated patients and objective cognitive impairment was observed in 36.1% of ICU-treated, 34.7% of ward-treated, and 8.9% of home-isolated patients. Subjective cognitive symptoms were associated with depressive and PTSD symptoms and female sex, but not with objective cognitive assessment or hospital metrics. Conclusions: One-third of COVID-19 patients, regardless of the acute disease severity, reported high levels of subjective cognitive dysfunction which was not associated with results from objective cognitive screening but with psychological and demographic factors. Our study stresses the importance of thorough assessment of patients reporting long-term subjective symptoms, screening for underlying mental health related factors such as PTSD or depression.Peer reviewe

Recall of facial expressions and simple orientations reveals competition for resources at multiple levels of the visual hierarchy

Many studies of visual working memory have tested humans' ability to reproduce primary visual features of simple objects, such as the orientation of a grating or the hue of a color patch, following a delay. A consistent finding of such studies is that precision of responses declines as the number of items in memory increases. Here we compared visual working memory for primary features and high-level objects. We presented participants with memory arrays consisting of oriented gratings, facial expressions, or a mixture of both. Precision of reproduction for all facial expressions declined steadily as the memory load was increased from one to five faces. For primary features, this decline and the specific distributions of error observed, have been parsimoniously explained in terms of neural population codes. We adapted the population coding model for circular variables to the non-circular and bounded parameter space used for expression estimation. Total population activity was held constant according to the principle of normalization and the intensity of expression was decoded by drawing samples from the Bayesian posterior distribution. The model fit the data well, showing that principles of population coding can be applied to model memory representations at multiple levels of the visual hierarchy. When both gratings and faces had to be remembered, an asymmetry was observed. Increasing the number of faces decreased precision of orientation recall, but increasing the number of gratings did not affect recall of expression, suggesting that memorizing faces involves the automatic encoding of low-level features, in addition to higher-level expression information.Peer reviewe

Statistical tests.

<p>Statistical tests.</p

Activity across visual areas.

<p><b>A)</b> Within the searchlight, t-value for average activity across different modulated shapes was calculated for each voxel and for each participant. Median t-values across participants are shown on the flattened Freesurfer average surface. Left and right hemispheres are on the left and right sides, respectively. <b>B)</b> Signal changes for circles and modulated shapes in different visual areas. <b>C)</b> Signal changes as a function of local curvature. Value 0.35 depicts circle shape. <b>D)</b> Signal changes as a function of radial frequency in different visual areas.</p

Stimuli.

<p><b>A)</b> Radial frequency patterns with different radial frequencies (3–6) and amplitudes (A1-4). <b>B)</b> All the different shapes were presented in four different orientations (polar phases 0, 90, 180 or 270 deg). In total, 65 different stimuli were used, circles and 64 modulated shapes (4 RFCs x 4 amplitudes x 4 orientations). <b>C)</b> RFC patterns are constructed by modulating a base circle with radial sine function. <b>D)</b> The concave and convex curvatures were calculated at the trough and peak, respectively, of the modulation function. Amplitude refers to the amount of modulation relative to the radius of base circle.</p

Model and measured RDMs.

<p>The RDMs describe the dissimilarity of the response patterns across different shapes. Five models were constructed based on the classification of the stimuli to four classes (<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004719#pcbi.1004719.t002" target="_blank">Table 2</a>) and one model was constructed by cross-correlating stimulus SF spectrum. Model RDMs for Radial Frequency, Amplitude, Convex Curvature, Contrast Energy, Spatial Frequency Spectrum, and Concave Curvature, and one example of the measured RDM from visual area V3AB. See <a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1004719#pcbi.1004719.s001" target="_blank">S1 Fig</a> for examples of measured RDMs in all areas.</p