Biology subjects

Schwarzkopf, D. S.

Publications and source records attributed to Schwarzkopf, D. S..

30 records · Page 2Linked to original sources

bioRxiv2022

Uncertain Precision: Neurobiological and Physiological Correlates of Conservative Confidence Bias

Correctly estimating the influence of uncertainty on our decisions is a critical metacognitive faculty. However, the relationship between sensory uncertainty (or its inverse, precision), decision accuracy, and subjective confidence is currently unclear. Although some findings indicate that healthy adults exhibit an illusion of over-confidence, under-confidence in response to sensory uncertainty has also been reported. One reason for this ambiguity is that stimulus intensity and precision are typically confounded with one another, limiting the ability to assess their independent contribution to metacognitive biases. Here we report four psychophysical experiments controlling these factors, finding that healthy human participants are systematically under-confident when discriminating low-precision stimuli. This bias remains even when decision accuracy and reaction time are accounted for, indicating that a performance-independent computation partially underpins the influence of sensory precision on confidence. We further show that this influence is linked to fluctuations in arousal and individual differences in the neuroanatomy of the left superior parietal lobe and middle insula. These results illuminate the neural and physiological correlates of precision misperception in metacognition. Significance StatementThe ability to recognize the influence of sensory uncertainty on our decisions underpins the veracity of self-monitoring, or metacognition. In the extreme, a systematic confidence bias can undermine decision accuracy and potentially underpin disordered self-insight in neuropsychiatric illness. Previously it was unclear if metacognition accurately reflects changes in sensory precision, in part due to confounding effects of stimulus intensity and precision. Here we overcome these limitations to repeatedly demonstrate a robust precision-related confidence bias. Further, we reveal novel neuroanatomical and physiological markers underlying this metacognitive bias. These results suggest a unique state-based computational mechanism may drive subjective confidence biases and further provide new avenues for investigating maladaptive awareness of uncertainty in neuropsychiatric disorders.

neuroscience↗

bioRxiv2021

Highly accurate retinotopic maps of the physiological blind spot in human visual cortex

The physiological blind spot is a naturally occurring scotoma corresponding with the optic disc in the retina of each eye. Even during monocular viewing, observers are usually oblivious to the scotoma, in part because the visual system extrapolates information from the surrounding area. Unfortunately, studying this visual field region with neuroimaging has proven difficult, as it occupies only a small part of retinotopic cortex. Here we used functional magnetic resonance imaging and a novel data-driven method for mapping the retinotopic organization in and around the blind spot representation in V1. Our approach allowed for highly accurate reconstructions of the extent of an observers blind spot, and out-performed conventional model-based analyses. This method opens exciting opportunities to study the plasticity of receptive fields after visual field loss, and our data add to evidence suggesting that the neural circuitry responsible for impressions of perceptual completion across the physiological blind spot most likely involves regions of extrastriate cortex - beyond V1.

neuroscience↗

bioRxiv2020

Flaws in Data Binning for Population Receptive Field Analyses

Data binning involves grouping observations into bins and calculating bin-wise summary statistics. It can cope with overplotting and noise, making it a versatile tool for comparing many observations. However, data binning goes awry if the same observations are used for binning (selection) and contrasting (selective analysis). This creates circularity, biasing noise components and resulting in artifactual changes in the form of regression towards the mean. Importantly, these artifactual changes are a statistical necessity. Here, we use (null) simulations and empirical repeat data to expose this flaw in the scope of post hoc analyses of population receptive field data. In doing so, we reveal that the type of data analysis, data properties, and circular data cleaning are factors shaping the appearance of such artifactual changes. We furthermore highlight that circular data cleaning and circular sorting of change scores are selection practices that result in artifactual changes even without circular data binning. These pitfalls might have led to erroneous claims about changes in population receptive fields in previous work and can be mitigated by using independent data for selection purposes. Our evaluations highlight the urgency for us researchers to make the validation of analysis pipelines standard practice. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=116 SRC="FIGDIR/small/422942v3_ufig1.gif" ALT="Figure 1"> View larger version (33K): org.highwire.dtl.DTLVardef@11c0c73org.highwire.dtl.DTLVardef@7583d3org.highwire.dtl.DTLVardef@121cf6dorg.highwire.dtl.DTLVardef@b9340d_HPS_FORMAT_FIGEXP M_FIG C_FIG HighlightsO_LICircular data binning produces artifactual changes in the form of regression towards the mean C_LIO_LIAnalysis type, data properties, and circular data cleaning shape these artifactual changes C_LIO_LICircular data cleaning and sorting produce artifactual changes even without circular data binning C_LI

neuroscience↗

bioRxiv2020

An absence of temporal filling-in at the physiological blind-spot.

Visual objects that extend across physiological blind spots seem to encapsulate the extent of blindness, due to a process commonly referred to as a perceptual filling-in of spatial vision. It is unclear if temporal perception is similar, so we examined temporal relationships governing causality perception across the blind spot. We found the human brain does not allow for the time an object should take to traverse the blind-spot when engaging in a causal interaction. We also used electroencephalogram (EEG), to examine temporal signatures of elements flickering on and off in tandem, or in counter-phase. At a control site, we found more brain activity was entrained at the duty cycle by flicker relative to counter-phase changes, whereas these conditions were indistinguishable about blind spots. Our data suggest a common pool of neurons might encode temporal properties on either side of physiological blind-spots. This would explain the absence of any allowance for the extent of blindness in causality perception, and the weakened differences between temporal representations of flicker and counter-phased changes about the blind spot. Overall, our data suggest that, unlike spatial vision, there is no temporal filling-in for perceptual representations about physiological blind spots.

physiology↗

bioRxiv2020

Heritability of visual cortex architecture and perception

How much of the functional organization of our visual system is inherited? Here we tested the heritability of retinotopic maps in human visual cortex using functional magnetic resonance imaging. We demonstrate that retinotopic organization shows a closer correspondence in monozygotic (MZ) compared to dizygotic (DZ) twin pairs, suggesting a partial genetic determination. Using population receptive field (pRF) analysis to examine the preferred spatial location and selectivity of these neuronal populations, we estimate a heritability around 30% for polar angle preferences and spatial selectivity, as quantified by pRF size, in extrastriate areas V2 and V3. Our findings are consistent with heritability in both the macroscopic arrangement of visual regions and stimulus tuning properties of visual cortex. This could constitute a neural substrate for variations in a range of perceptual effects, which themselves have been found to be at least partially genetically determined. These findings also add convergent evidence for the hypothesis that functional map topology is linked with cortical morphology. HighlightsO_LIWe analyzed retinotopic maps from monozygotic and dizygotic twin pairs C_LIO_LIVisual field maps in V1-V3 are more similar in monozygotic twins C_LIO_LIHeritability is greater in V1 and V3 for polar angle and population receptive field sizes C_LIO_LIEccentricity maps show lesser degree of heritability C_LIO_LIFurther evidence for link between cortical morphology and topology of retinotopic maps C_LI Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=182 HEIGHT=200 SRC="FIGDIR/small/077545v4_ufig1.gif" ALT="Figure 1"> View larger version (77K): org.highwire.dtl.DTLVardef@ceacd6org.highwire.dtl.DTLVardef@b51604org.highwire.dtl.DTLVardef@b860f8org.highwire.dtl.DTLVardef@e67398_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2019

Topographic Signatures of Global Object Perception in Human Visual Cortex

Our visual system readily groups dynamic fragmented input into global objects. How the brain represents such perceptual grouping remains however unclear. To address this question, we recorded brain responses using functional magnetic resonance imaging whilst observers perceived a dynamic bistable stimulus that could either be perceived globally (i.e., as a grouped and coherently moving shape) or locally (i.e., as ungrouped and incoherently moving elements). We further estimated population receptive fields and used these to back-project the brain activity during stimulus perception into visual space via a searchlight procedure. Global perception resulted in non-topographic suppression of responses in lower visual cortex accompanied by wide-spread enhancement in higher object-sensitive cortex. However, follow-up experiments indicated that higher object-sensitive cortex is suppressed if global perception lacks shape grouping, and that grouping-related suppression can be diffusely confined to stimulated sites once stimulus size is reduced. These results speak against a rigid between-area response amplitude code acting as a generic grouping mechanism and point to a within-area response amplitude code mediating the perception of figure and ground.

neuroscience↗

bioRxiv2019

Mapping sequences can bias population receptive field estimates

Population receptive field (pRF) modelling is a common technique for estimating the stimulus-selectivity of populations of neurons using neuroimaging. Here, we aimed to address if pRF properties estimated with this method depend on the spatio-temporal structure and the predictability of the mapping stimulus. We mapped the polar angle preference and tuning width of voxels in visual cortex (V1-V4) of healthy, adult volunteers. We compared sequences orderly sweeping through the visual field or jumping from location to location employing stimuli of different width (45{degrees} vs 6{degrees}) and cycles of variable duration (8s vs 60s). While we did not observe any systematic influence of stimulus predictability, the temporal structure of the sequences significantly affected tuning width estimates. Ordered designs with large wedges and short cycles produced systematically smaller estimates than random sequences. Interestingly, when we used small wedges and long cycles, we obtained larger tuning width estimates for ordered than random sequences. We suggest that, ordered and random mapping protocols show different susceptibility to other design choices such as stimulus type and duration of the mapping cycle and can produce significantly different pRF results.

neuroscience↗

bioRxiv2019

Altered visual population receptive fields in human albinism

1Albinism is a congenital disorder where misrouting of the optic nerves at the chiasm gives rise to abnormal visual field representations in occipital cortex. In typical human development, the left occipital cortex receives retinal input predominantly from the right visual field, and vice-versa. In albinism, there is a more complete decussation of optic nerve fibers at the chiasm, resulting in partial representation of the temporal hemiretina (ipsilateral visual field) in the contralateral hemisphere. In this study, we characterize the receptive field properties for these abnormal representations by conducting detailed fMRI population receptive field mapping in a rare subset of participants with albinism and no ocular nystagmus. We find a nasal bias for receptive field positions in the abnormal temporal hemiretina representation. In addition, by modelling responses to bilateral visual field stimulation in the overlap zone, we found evidence in favor of discrete unilateral receptive fields, suggesting a conservative pattern of spatial selectivity in the presence of abnormal retinal input. HighlightsO_LIWe characterized population receptive fields in albinotic participants with no ocular nystagmus C_LIO_LIConfirmed overlapping representations of left and right visual fields in cortex C_LIO_LIDetected nasal bias in receptive field location for temporal hemiretina representation C_LIO_LIEvidence in favor of discrete unilateral receptive fields and against double coding C_LI

neuroscience↗

bioRxiv2019

Comparison of human population receptive field estimates between scanners and the effect of temporal filtering

Population receptive field (pRF) analysis with functional magnetic resonance imaging (fMRI) is an increasingly popular method for mapping visual field representations and estimating the spatial selectivity of voxels in human visual cortex. However, the multitude of experimental setups and processing methods used makes comparisons of results between studies difficult. Here, we show that pRF maps acquired in the same three individuals using comparable scanning parameters on a 1.5 and a 3 Tesla scanner located in two different countries are very similar. As expected, the signal-to-noise ratio for the 3 Tesla data was superior; critically, however, estimates of pRF size and cortical magnification did not reveal any systematic differences between the sites. Moreover, we tested the effect of low-pass filtering of the time series on pRF estimates. Unsurprisingly, filtering enhanced goodness-of-fit, presumably by removing high-frequency noise. However, there was no substantial increase in the number of voxels containing meaningful retinotopic signals after low-pass filtering. Importantly, filtering also increased estimates of pRF size in the early visual areas which could substantially skew interpretations of spatial tuning properties. Our results therefore suggest that pRF estimates are generally comparable between scanners of different field strengths, but temporal filtering should be used with caution.\n\nPrecisPopulation Receptive Field mapping performed with similar protocols at two different sites, a 1.5T MRI scanner in London, and a 3T scanner in Auckland, yielded comparable results. Temporal filtering of the fMRI time course increased concordance of modelled pRFs, but introduced a bias in pRF size.

neuroscience↗

bioRxiv2018

Individual differences in visual salience vary along semantic dimensions

What determines where we look? Theories of attentional guidance hold that image features and task demands govern fixation behaviour, while differences between observers are noise. Here, we investigated the fixations of > 100 human adults freely viewing a large set of complex scenes. We found systematic individual differences in fixation frequencies along six semantic stimulus dimensions. These differences were large (> twofold) and highly stable across images and time. Surprisingly, they also held for first fixations directed towards each image, commonly interpreted as bottom-up visual salience. Their perceptual relevance was documented by a correlation between individual face salience and recognition skills. The dimensions of individual salience and their covariance pattern replicated across samples from three different countries, suggesting they reflect fundamental biological mechanisms of attention. Our findings show stable individual salience differences along semantic dimensions, with meaningful perceptual implications. Salience reflects features of the observer as well as the image.

neuroscience↗

bioRxiv2018

Population receptive field estimates for motion-defined stimuli

The processing of motion changes throughout the visual hierarchy, from spatially restricted local motion in early visual cortex to more complex large-field global motion at later stages. Here we used functional magnetic resonance imaging (fMRI) to examine spatially selective responses in these areas related to the processing of random-dot stimuli defined by differences in motion. We used population receptive field (pRF) analyses to map retinotopic cortex using bar stimuli comprising coherently moving dots. In the first experiment, we used three separate background conditions: no background dots (dot-defined bar-only), dots moving coherently in the opposite direction to the bar (kinetic boundary) and dots moving incoherently in random directions (global motion). Clear retinotopic maps were obtained for the bar-only and kinetic-boundary conditions across visual areas V1-V3 and in higher dorsal areas. For the global-motion condition, retinotopic maps were much weaker in early areas and became clear only in higher areas, consistent with the emergence of global-motion processing throughout the visual hierarchy. However, in a second experiment we demonstrate that this pattern is not specific to motion-defined stimuli, with very similar results for a transparent-motion stimulus and a bar defined by a static low-level property (dot size) that should have driven responses particularly in V1. We further exclude explanations based on stimulus visibility by demonstrating that the observed differences in pRF properties do not follow the ability of observers to localise or attend to these bar elements. Rather, our findings indicate that dorsal extrastriate retinotopic maps may primarily be determined by the visibility of the neural responses to the bar relative to the background response (i.e. neural signal-to-noise ratios) and suggests that claims about stimulus selectivity from pRF experiments must be interpreted with caution.

neuroscience↗

bioRxiv2017

Population receptive field tuning properties of visual cortex during childhood

Improvements in visuospatial perception such as contrast sensitivity and Vernier acuity continue until late in childhood, but the neural mechanisms driving these age-related changes are currently unclear. One contributing factor could be the protracted development of spatial tuning of neuronal populations across the visual cortex. Here we tested this possibility using population receptive field (pRF) mapping (Dumoulin and Wandell, 2008) in 6-to 12-year-old children and adults. We fitted pRF models to BOLD signals measured in areas V1-V4 and V3a during fMRI whilst participants watched wedge and ring stimuli traversing the visual field. Cortical magnification and the width of pRF tuning functions changed with viewing eccentricity in all participants. However, there were no age-related changes in pRF size, shape, cortical magnification, or map consistency across any of the visual areas measured. These results suggest that visuospatial perception in late childhood beyond age 6 years is not substantially limited by low-level spatial tuning properties of neuronal populations in visual cortex. Instead, performance improvements in this period may reflect more efficient use of the spatial information available in the visual system when forming perceptual judgments. These findings are an important step towards disentangling which neural mechanisms contribute to the eventual emergence of mature spatial vision, and for understanding the processes that determine the scope for visual plasticity at different stages of life.

neuroscience↗