Biology subjects

Rademaker, R. L.

Publications and source records attributed to Rademaker, R. L..

9 recordsLinked to original sources

bioRxiv2026

Converting color memory toward a spatial format to benefit behavior

Visual working memory allows for the brief maintenance of information to serve behavioral goals. It has been shown that when the specific action required to serve a future goal is predictable, people can flexibly change a visual memory representation to incorporate an action-based one, demonstrating the goal-oriented nature of visual working memory. Can such flexibility also be observed within the visual domain, between color and space? In this eye-tracking study, participants remembered either a centrally presented color or a spatial position around fixation. Critically, when remembering a color the response wheel was either randomly rotated, or shown at a fixed rotation, on every trial. When fixed, every target color could be associated with a predictable position on the wheel during response. Do people incorporate this added spatial information in their behavior? Participants utilized color-space associations when remembering color: Response initiation happened faster when the color wheel was fixed compared to random, irrespective of whether an action could be planned or not. Next, we showed that gaze was biased towards the position of the spatial memory target during the delay, extending previous work on gaze biases. Importantly, also when remembering a color, gaze was biased towards the anticipated position of that color on the response wheel when it was fixed. Together, our results show a behavioral benefit of added spatial information for color memory, and systematic changes in gaze that reflect flexible utilization of space.

neuroscience↗

bioRxiv2025

Top-down feedback can explain the existence of working memory traces in early visual cortex

The temporary storage of visual memories is known to engage early visual cortex (EVC), where mnemonic content is presumed to be stored in weak or latent states. Two mechanisms have been suggested to underlie this storage: Top-down feedback from anterior cortical sites, and short-term synaptic plasticity (STSP) traces laid down by previous sensory inputs. Here, we tested if these mechanisms can account for two hallmarks of working memory, namely, the flexible selection of information from working memory, and the robustness of working memory against distraction. Simulating firing rates in a neural network model of working memory, we show that STSP cannot easily account for selection of information from within the working memory store, and is not robust to visual distraction. Rather, any input that passes through the visual system is briefly remembered, irrespective of its relevance. In contrast, top-down feedback can establish durable mnemonic signals in EVC that reflect currently task-relevant working memory contents and are robust to distraction. We argue that feedback is a parsimonious explanation for the existence of mnemonic signals in EVC, given that the storage of working memories is distributed across a hierarchy of cortical sites, which are known to have widespread feedback projections to visual cortex.

neuroscience↗

bioRxiv2025

Visual representations in the human brain rely on a reference frame that is in between allocentric and retinocentric coordinates

Visual information in our everyday environment is anchored to an allocentric reference frame - a tall building remains upright even when you tilt your head, which changes the projection of the building on your retina from a vertical to a diagonal orientation. Does retinotopic cortex represent visual information in an allocentric or retinocentric reference frame? Here, we investigate which reference frame the brain uses by dissociating allocentric and retinocentric reference frames via a head tilt manipulation combined with electroencephalography (EEG). Nineteen participants completed between 1728-2880 trials during which they briefly viewed (150 ms) and then remembered (1500 ms) a randomly oriented target grating. In interleaved blocks of trials, the participants head was either kept upright, or tilted by 45{o} using a custom rotating chinrest. The target orientation could be decoded throughout the trial (using both voltage and alpha-band signals) when training and testing within head-upright blocks, and within head-tilted blocks. Importantly, we directly addressed the question of reference frames via cross-generalized decoding: If target orientations are represented in a retinocentric reference frame, a decoder trained on head-upright trials would predict a 45{o} offset in decoded orientation when tested on head-tilted trials (after all, a vertical building becomes diagonal on the retina after head tilt). Conversely, if target representations are allocentric and anchored to the real world, no such offset should be observed. Our analyses reveal that from the earliest stages of perceptual processing all the way throughout the delay, orientations are represented in between an allocentric and retinocentric reference frame. These results align with previous findings from physiology studies in non-human primates, and are the first to demonstrate that the human brain does not rely on a purely allocentric or retinocentric reference frame when representing visual information.

neuroscience↗

bioRxiv2024

Manipulating attentional priority creates a trade-off between memory and sensory representations in human visual cortex

People often remember visual information over brief delays while actively engaging with ongoing inputs from the surrounding visual environment. Depending on the situation, one might prioritize mnemonic contents (i.e., remembering details of a past event), or preferentially attend sensory inputs (i.e., minding traffic while crossing a street). Previous fMRI work has shown that early visual areas can simultaneously represent both mnemonic and passively viewed visual information. Here we test the limits of such simultaneity by manipulating attention towards visual distractors during a working memory task performed by human subjects undergoing fMRI scanning. Participants remembered the orientation of a target grating while a distractor grating was shown throughout most of the memory delay. Critically, there were several subtle changes in the contrast and the orientation of the distractor, and participants were cued to either ignore the distractor, detect a change in contrast, or detect a change in orientation. Despite visual stimulation being matched in all three conditions, the fidelity of memory representations in early visual cortex was highest when the distractor was ignored, intermediate when participants attended distractor contrast, and lowest when participants attended the orientation of the distractor during the delay. In contrast, the fidelity of distractor representations was lowest when ignoring the distractor, intermediate when attending distractor-contrast, and highest when attending distractor-orientation. These data suggest a trade-off in early sensory representations when engaging top-down feedback to attend both seen and remembered features, and may partially explain memory failures that occur when subjects are distracted by external events.

neuroscience↗

bioRxiv2024

Model mimicry limits conclusions about neural tuning and can mistakenly imply unlikely priors

In a recent issue of Nature Communications, Harrison, Bays, and Rideaux1 use electroencephalography (EEG) to infer population tuning properties from human visual cortex, and deliver a major update to existing knowledge about the most elemental building block of visual perception - orientation tuning. Using EEG together with simulations in an approach they refer to as "generative forward modeling", the authors adjudicate between two competing population tuning schemes for orientation tuning in visual cortex. They claim that a redistribution of orientation tuning curves can explain their observed pattern of EEG results, and that this tuning scheme embeds a prior of natural image statistics that exhibits a previously undiscovered anisotropy between vertical and horizontal orientations. If correct, this approach could become widely used to find unique neural coding solutions to population response data (e.g., from EEG) and to yield a "true" population tuning scheme deemed generalizable to other instances. However, here we identify major flaws that invalidate the promise of this approach, which we argue should not be used at all. First, we will examine the premise of Harrison and colleagues1, to subsequently explain why "generative forward modeling" cannot circumvent model mimicry pitfalls and can deliver many possible solutions of unknowable correctness. Finally, we show a tentative alternative explanation for the data. Conflict of interestThe authors declare no conflict of interest

neuroscience↗

bioRxiv2023

A gradual transition from veridical to categorical representations along the visual hierarchy during working memory, but not perception.

The ability to stably maintain visual information over brief delays is central to healthy cognitive functioning, as is the ability to differentiate such internal representations from external inputs. One possible way to achieve both is via multiple concurrent mnemonic representations along the visual hierarchy that differ systematically from the representations of perceptual inputs. To test this possibility, we examine orientation representations along the visual hierarchy during perception and working memory. Human participants directly viewed, or held in mind, oriented grating patterns, and the similarity between fMRI activation patterns for different orientations was calculated throughout retinotopic cortex. During direct viewing of grating stimuli, similarity was relatively evenly distributed amongst all orientations, while during working memory the similarity was higher around oblique orientations. We modeled these differences in representational geometry based on the known distribution of orientation information in the natural world: The "veridical" model uses an efficient coding framework to capture hypothesized representations during visual perception. The "categorical" model assumes that different "psychological distances" between orientations result in orientation categorization relative to cardinal axes. During direct perception, the veridical model explained the data well. During working memory, the categorical model gradually gained explanatory power over the veridical model for increasingly anterior retinotopic regions. Thus, directly viewed images are represented veridically, but once visual information is no longer tethered to the sensory world there is a gradual progression to more categorical mnemonic formats along the visual hierarchy.

neuroscience↗

bioRxiv2021

Flexible utilization of spatial- and motor-based codes for the storage of visuo-spatial information

Working memory provides flexible storage of information in service of upcoming behavioral goals. Some models propose specific fixed loci and mechanisms for the storage of visual information in working memory, such as sustained spiking in parietal and prefrontal cortex during working memory maintenance. An alternative view is that information can be remembered in a flexible format that best suits current behavioral goals. For example, remembered visual information might be stored in sensory areas for easier comparison to future sensory inputs, or might be re-coded into a more abstract action-oriented format and stored in motor areas. Here, we tested this hypothesis using a visuo-spatial working memory task where the required behavioral response was either known or unknown during the memory delay period. Using fMRI and multivariate decoding, we found that there was less information about remembered spatial position in early visual and parietal regions when the required response was known versus unknown. Further, a representation of the planned motor action emerged in primary somatosensory, primary motor, and premotor cortex during the same task condition where spatial information was reduced in early visual cortex. These results suggest that the neural networks supporting working memory can be strategically reconfigured depending on specific behavioral requirements during a canonical visual working memory paradigm.

neuroscience↗

bioRxiv2018

Faded visual afterimages reappear after TMS over early visual cortex

In the complete absence of small transients in visual inputs (e.g. by experimentally stabilizing an image on the retina, or in everyday life during intent staring), information perceived by the eyes will fade from the perceptual experience. While the mechanisms of visual fading remain poorly understood, one possibility is that higher-level brain regions actively suppress the stable visual signals via targeted inhibitory feedback onto Early Visual Cortex (EVC). Here, we used positive afterimages and multisensory conflict to induce gestaltlike fading of participants own hands. In two separate experiments, participants rated the perceived quality of their hands both before and after Transcranial Magnetic Stimulation (TMS) was applied over EVC. In a first experiment, triple pulse TMS was able to make a faded hand appear less faded after the pulses were applied, compared to placebo pulses. A second experiment demonstrated that this was because triple pulse TMS inoculated the removed hand from fading over time. Interestingly, TMS similarly affected the left and right hand, despite being applied only over right EVC. Together, our results suggest that TMS can lift inhibitory processes in EVC and reverse the effects of visual fading. And it might do so by crossing transcollosal connections, or via multimodal integration sites in which both hands are represented.

neuroscience↗

bioRxiv2018

Simultaneous representation of sensory and mnemonic information in human visual cortex

Traversing sensory environments requires keeping relevant information in mind while simultaneously processing new inputs. Visual information is kept in working memory via feature selective responses in early visual cortex, but recent work had suggested that new sensory inputs wipe out this information. Here we show region-wide multiplexing abilities in classic sensory areas, with population-level response patterns in visual cortex representing the contents of working memory concurrently with new sensory inputs.

neuroscience↗