Biology subjects

Carrasco, M.

Publications and source records attributed to Carrasco, M..

At least 19 recordsLinked to original sources

bioRxiv2026

Featural representation and internal noise around the visual field

In human adults, visual performance varies systematically around the visual field. It is higher along the horizontal than the vertical meridian (horizontal-vertical anisotropy, HVA) and higher at the lower than the upper vertical meridian (vertical-meridian asymmetry, VMA). Although these robust performance fields have been linked to non-uniform neural resources, the system-level computations that translate neural constraints into perceptual asymmetries remain largely unexplored. Here, we used reverse correlation to characterize feature weighting and internal noise during peripheral orientation detection. Reverse correlation revealed non-ideal feature weighting in the joint orientation-spatial-frequency space, which was incorporated into a noisy-observer model jointly constrained by trial-wise detection responses and double-pass consistency. Across observers, the magnitude of the HVA in contrast sensitivity was correlated with individual asymmetries in orientation sensitivity and additive internal noise. In contrast, we found limited evidence that any tested representational or noise components reliably accounted for individual differences in VMA magnitude. Spatial-frequency tuning exhibited substantial individual variability, often peaking below the signals spatial frequency, but did not vary systematically across locations or explain performance asymmetries. These findings suggest that the HVA reflects systematic variation in the feature weighting of task-relevant orientations and internal noise, while constraining which computational components provide robust explanations of polar-angle asymmetries. Moreover, our framework provides a principled approach that links this prevalent perceptual asymmetry to the system-level computations that transform sensory information into perceptual decisions. Author summaryHuman vision is surprisingly uneven across our field of view. At the same distance from where we look, vision is better along the horizontal axis than the vertical axis, and better in the lower than the upper half of the vertical axis. These differences are well established, but little is known about their computational basis. To investigate, we combined visual detection tasks with computational modeling. By analyzing how observers detected faint patterns within noisy images, we measured how they process distinct features--like patterns with different orientations and spatial frequencies at different visual field locations. We then fit a mathematical model to separate distinct sources of internal noise. We found that differences in how the brain processes line orientations predicted the magnitude of the horizontal-vertical asymmetry across individuals, whereas distinct components of internal noise predicted these asymmetries in different ways. Our results show that visual field asymmetries are not driven by a single visual bottleneck, but rather by location-specific combinations of how the brain encodes relevant feature information and neural noise. This study helps explain why human vision is fundamentally uneven across our field of view.

neuroscience↗

bioRxiv2026

Endogenous attention is invariant to sequential effects in performance around the visual field

Covert spatial attention selects and prioritizes relevant sensory information. Endogenous attention is voluntary, goal-driven, and flexible. However, it cannot alleviate visual polar-angle asymmetries, specifically, the horizontal-vertical anisotropy and the vertical meridian asymmetry. Visual perception is affected by both current sensory inputs and contextual information over time and space, such as the perception of preceding trials. Previous studies reported sequential effects whereby attention interacts with response repetitions. But it is unknown whether and how endogenous attention modulation on performance varies as a function of target location and trial history. Here, we reanalyzed data from three published studies of endogenous attention in orientation discrimination tasks, to (1) assess the typical sequential effects on response, in which response to the current trial is biased toward the previous one, and (2) examine if sequential effects would modulate the performance across locations, across four dimensions: (1) location, (2) feature, (3) attention repetition condition, and (4) the correctness of the preceding (n -1) trial. First, we demonstrated typical sequential effects of response repetition to the repeated location and feature aspects of the target. Second, we found a robust effect of attention on performance, but the results did not reveal evidence of sequential attention effects as a function of the four dimensions in any of the three studies. Moreover, there were no interactions between attention and location when considering trial history. Together, these findings provide compelling evidence that visual polar-angle asymmetries are resistant to endogenous attention, and that even top- down factors-sequential effects-do not alleviate these asymmetries in performance.

neuroscience↗

bioRxiv2026

Transcranial magnetic stimulation to frontal cortex, unlike occipital stimulation, does not disrupt exogenous attention

Orienting covert attention to a target location improves performance across a wide array of visual tasks [1, 2]. Whereas fMRI studies have identified partially overlapping frontoparietal networks underlying endogenous (voluntary) and exogenous (involuntary) covert attention, these correlational methods cannot establish whether a given region is functionally necessary. Prior neurostimulation studies have established that early visual cortex (V1/V2) is critical for exogenous [3, 4] but not endogenous attention [5], whereas the right frontal eye field (rFEF+) is critical for endogenous attention [5]. Here, we used a combined psychophysical-TMS protocol to investigate whether rFEF+ is also required for exogenous attention. Participants performed an orientation discrimination task, in which a peripheral cue (valid, neutral, or invalid) preceded a target and a distractor stimulus. We applied two successive TMS pulses to rFEF+ during stimulus presentation and measured contrast-response functions (CRFs) to quantify perceptual sensitivity (d') across all attention cueing and stimulation conditions. When the distractor was stimulated, exogenous attention yielded a characteristic response gain at the target--with performance benefits for valid cues and costs for invalid cues at high contrast levels. Crucially, this response gain was entirely preserved when the target was stimulated. This pattern contrasts with previous findings demonstrating that TMS to V1/V2 eliminates exogenous attentional effects at the stimulated location. These results indicate that rFEF+ is not necessary for exogenous attention, and together with previous studies [3-5] complete a double dissociation: rFEF+ is critical for endogenous but not exogenous attention, whereas V1/V2 is critical for exogenous but not endogenous attention. These findings reveal a distinct causal cortical architecture for voluntary and involuntary spatial attention, suggesting that they rely on different cortical scaffolds.

neuroscience↗

bioRxiv2026

A retinotopic wiring principle of the human brain

Summary paragraphA central challenge in neuroscience is to understand how anatomical connectivity links neural representations to behavior. In sensory systems, cortical areas encode structured maps of the external world, yet it remains unclear whether and how this representational geometry constrains long-range connectivity in the living human brain. Here, we show that structural connectivity in the human visual cortex preserves retinotopic organization, revealing a retinotopic wiring principle; cortical regions representing the same locations in visual space preferentially connect. Across more than 1,700 participants spanning ages 2 to 88 years, we further show that well-known perceptual asymmetries correspond to systematic asymmetries in connectivity within early visual cortex, but not in connections linking visual cortex to the rest of the brain. We introduce a scalable approach to map retinotopic connectivity when tractography alone is unreliable. Together, these findings demonstrate that anatomical connectivity preserves the geometry of neural representations, providing a general principle linking brain structure, function, and behavior.

neuroscience↗

bioRxiv2026

Dynamic cortical routing mediates temporal attention

Selecting information from dynamic streams requires mechanisms that prioritize a visual stimulus at a specific moment over preceding and subsequent stimuli at the same location. Whereas selective temporal attention has been found to enhance neural responses to stimuli, its impact on communication between brain regions remains unexplored. Here, we investigated whether prioritizing a stimulus at a specific time is achieved through selective routing of stimulus information across cortical networks using MEG. We developed a dynamic informational connectivity approach to quantify shared stimulus information between each region and the rest of the network. When stimuli compete in time, we found that temporal attention modulated the network at both early and late post-target time windows, routing information along two possible pathways--occipito-fronto-cingulate and occipito-temporal--via both transient bursts of network communication and theta-rhythmic replay. These results provide evidence that under dynamic sensory input, the timing of neural communication determines stimulus selection.

neuroscience↗

bioRxiv2025

Polar angle asymmetries persist despite covert spatial attention and differential adaptation

Visual adaptation and attention are two processes that help manage the brains limited bioenergetic resources for perception. Visual perception is heterogeneous around the visual field: it is better along the horizontal than the vertical meridian (horizontal-vertical anisotropy, HVA), and better along the lower than the upper vertical meridian (vertical meridian asymmetry, VMA). Recently, we showed that visual adaptation is more pronounced at the horizontal than the vertical meridian, but whether and how this differential adaptation modulates the effects of covert spatial attention remains unknown. In this study, we investigated whether and how the effects of endogenous (voluntary) and exogenous (involuntary) covert attention on an orientation discrimination task vary at the cardinal meridians, with and without adaptation. We manipulated endogenous (Experiment 1) or exogenous (Experiment 2) attention via an informative central or uninformative peripheral cue, respectively. Results showed that (1) in the non-adapted condition, the typical HVA and VMA emerged in contrast thresholds; (2) the adaptation effect was stronger at the horizontal than the vertical meridian; and (3) regardless of adaptation, both endogenous and exogenous attention enhanced and impaired performance at the attended and unattended locations, respectively, to a similar degree at both cardinal meridians. Together, these findings reveal that, despite differences between endogenous and exogenous attention, their effects remain uniform across cardinal meridians-even under differential adaptation that reduces intrinsic asymmetries of visual field representations.

neuroscience↗

bioRxiv2025

System-Level Computations Underlie Visual Field Heterogeneity

Human visual perception for basic dimensions varies with eccentricity and polar angle, influencing daily activities such as reading, searching and scene perception. We investigated whether and how system-level computations that transform visual input into perception underlie these heterogeneities. Using the equivalent noise method and perceptual template model, we estimated gain, internal noise, and nonlinearity for orientation discrimination across eccentricity (fovea, parafovea and perifovea) and around polar angle. Participants discriminated the orientation of Gabors embedded in dynamic white noise and showed the expected variations across eccentricity and around polar angle. Importantly, visual performance declined with eccentricity due to decreased gain and nonlinearity and increased internal noise. Observers with stronger eccentricity effects showed greater gain decrease. Only gain varied with polar angle--higher along the horizontal than vertical meridian, and lower than upper vertical meridian--paralleling performance asymmetries. This dissociation aligns with known variations in neuronal count and tuning, suggesting that neural correlations and neural noise contribute to these system-level computations. By revealing distinct system-level computations underlying the eccentricity effect and polar angle asymmetries, our findings link perceptual heterogeneity across the visual field and neural architecture and provide insights into how the human brain encodes information under neural constraints. Significance StatementHuman visual performance varies across eccentricity-distance from gaze-and around polar angle -circular dimension. Retinal factors and cortical surface area account for eccentricity, but only partially for polar angle variations. Here, we show that system-level computations--how signal are amplified and how noisy the system is--distinctly underlie these perceptual variations. Decline across eccentricity stems from both reduced gain and nonlinearity and elevated internal noise, whereas variation around polar angle arises solely from gain difference. This dissociation implies fundamental differences in information processing along two axes of the visual field. Our results provide a computational link between behavior and its neural bases and highlight the importance of considering both eccentricity and polar angle in modeling and understanding human perception.

neuroscience↗

bioRxiv2025

Visual Field Inhomogeneities Shape Visual Working Memory

Whether the primary visual cortex (V1) is essential for visual working memory (vWM) remains a topic of scientific debate. The current study expanded upon previous findings by examining whether idiosyncratic architectural properties of V1, particularly those underlying visual field inhomogeneities such as polar angle asymmetries, predict interindividual differences in vWM performance. A total of 292 participants underwent quantitative MRI (qMRI) using a multiparametric mapping sequence to generate four microstructural maps per participant: magnetization transfer (MT), proton density (PD), longitudinal relaxation rate (R1), and transverse relaxation rate (R2*). In a separate session, the participants completed a vWM task designed to probe visual field inhomogeneities. Behavioral results are consistent with previously reported asymmetries in vWM, particularly the inverted polarity of the vertical meridian asymmetry (VMA). Quantitative MRI analysis revealed significant associations between VMA and multiple qMRI parameters within V1, indicating that V1 microarchitecture contributes to variability in vWM performance. Additionally, cortical thickness measures linked V3 to left-right asymmetry, suggesting that structural variability in the early visual cortex beyond V1 also shapes vWM performance. These findings are consistent with the sensory recruitment hypothesis and demonstrate that fine-grained architectural characteristics of early visual areas constrain vWM performance.

neuroscience↗

bioRxiv2025

Preferred spatial frequency covaries with cortical magnification in human primary visual cortex

Primary visual cortex (V1) has long served as a model system for understanding cortical organization. Although its structural and functional properties vary markedly across its surface, patterns of covariation suggest possible underlying constancies. Such constancies would imply that V1 is composed of multiple identical units whose visual properties differ only due to differences in their inputs. To test this, we used fMRI to investigate how V1 cortical magnification and preferred spatial frequency covary with eccentricity and polar angle, measured in 40 observers. V1 cortical magnification and preferred spatial frequency were strongly correlated across eccentricity and around polar angle, however their relation differed between these dimensions: they were proportional across eccentricity but not polar angle. The constant ratio of cortical magnification to preferred spatial frequency when measured as a function of eccentricity suggests a shared underlying cause of variation in the two properties, e.g., the gradient of retinal ganglion cell density across eccentricity. In contrast, the deviation from proportionality around polar angle implies that cortical variation differs from that in retina along this dimension. Thus, a constancy hypothesis is supported for one of the two spatial dimensions of V1, highlighting the importance of examining the full 2D-map to understand how V1 is organized. AUTHOR SUMMARYHuman primary visual cortex (V1) is the first region of the brain to receive visual input. Its organization, whether built from uniform repeating units or following more complex patterns, remains debated. We assessed this by measuring two key V1 properties: cortical magnification (how much cortex processes each region of the visual field) and preferred spatial frequency (the level of detail neurons respond best to). Using MRI, we found these properties are closely linked, but their relation differs by visual field dimension. Across eccentricity (distance from the center of gaze), the two properties decrease at a fixed ratio, reflecting structural patterns in the retina. Around polar angle (circular dimension), this proportionality no longer holds, even though the two properties still covary. These results show that whereas V1 is partly governed by a simple rule of proportionality, its organization cannot be explained as just repeating units. Instead, different spatial dimensions follow different principles, emphasizing the need to consider the full two-dimensional layout of the visual map to understand how vision is represented in the brain.

neuroscience↗

bioRxiv2025

Visual adaptation stronger at horizontal than vertical meridian: Linking performance with V1 cortical surface area

Visual adaptation reduces bioenergetic expenditure by decreasing sensitivity to repetitive and similar stimuli. In human adults, visual performance varies systematically around polar angle for many visual dimensions and tasks: Performance is superior along the horizontal than the vertical meridian (horizontal-vertical anisotropy, HVA), and the lower than upper vertical meridian (vertical meridian asymmetry, VMA). These asymmetries are resistant to spatial and temporal attention. However, it remains unknown whether visual adaptation differs around polar angle. Here, we investigated how adaptation influences contrast sensitivity at the fovea and perifovea across the four cardinal meridian locations, for both horizontal and vertical stimuli in an orientation discrimination task. In the non-adapted conditions, the HVA was more pronounced for horizontal than vertical stimuli. For both orientations, adaptation was stronger along the horizontal than vertical meridian, exceeding foveal adaptation. Additionally, perifoveal adaptation effects positively correlated with individual V1 cortical surface area. These findings reveal that visual adaptation mitigates the HVA in contrast sensitivity, fostering perceptual uniformity around the visual field while conserving bioenergetic resources.

neuroscience↗

bioRxiv2025

Temporal attention and oculomotor effects dissociate distinct types of temporal expectation

Temporal expectation-the ability to predict when events occur-relies on probabilistic information within the environment. Two types of temporal expectation, temporal precision, based on the variability of an events onset, and hazard rate, based on the increasing probability of an event with onset delay, interact with temporal attention-ability to prioritize specific moments- at the performance level: Attentional benefits increase with precision but diminish with hazard rate. Both temporal expectation and temporal attention improve fixational stability; however, the distinct oculomotor effects of temporal precision and hazard rate, as well as their interactions with temporal attention, remain unknown. Investigating microsaccade dynamics, we found that hazard-based expectations were reflected in the oculomotor responses, whereas precision-based expectations emerged only when temporal attention was deployed. We also found perception-eye movement dissociations for both types of temporal expectation, yet attentional benefits in performance coincided with microsaccade rate modulations. These findings reveal an interplay among distinct types of temporal expectation and temporal attention in enhancing and recalibrating fixational stability.

neuroscience↗

bioRxiv2025

Leishmania tarentolae and Leishmania infantum in geckos from Mallorca Island, Spain

Leishmania tarentolae and Leishmania infantum are two sympatric parasites of significant ecological and epidemiological interest in the Mediterranean basin. This study investigated the prevalence of L. tarentolae and L. infantum in two gecko species (Tarentola mauritanica and Hemidactylus turcicus) present on Mallorca Island, Spain, using duplex quantitative PCR. A total of 59 geckos were sampled across the island, including 53 T. mauritanica and six H. turcicus. Tissue and blood samples were screened for both parasites, and generalized linear models were used to assess organ-specific infection patterns. The results revealed the prevalence of Leishmania infection in adult T. mauritanica, with 10/49 (20.41%) testing positive for L. tarentolae and with 1/49 (2.04%) for L. infantum. Coinfection with both parasites was detected in 3/49 geckos (6.12%). No positives were identified in H. turcicus, probably due to small sample size. Regarding positivity by tissues, coleomic organs were more likely to be positive for L. tarentolae in adult T. mauritanica than blood, with a slighter positivity in the liver, spleen and lung. Interestingly, L. infantum was detected more frequently coinfecting with L. tarentolae than as a single parasite. These prevalence rates and the existence of coinfections highlight potential ecological interactions between the two parasites and reptiles. This study provides valuable data on the potential role of geckos in endemic areas like Mallorca. Author SummaryLeishmaniosis is a zoonotic disease caused by parasites that can infect both animals and humans. In Europe, Leishmania infantum is the main species responsible for the disease, with dogs acting as its primary host. However, recent research suggests that other animals, including reptiles, might also play a role in their spread. In this study, centered in wild geckos from Mallorca Island (Spain), we investigated the prevalence of L. tarentolae and L. infantum in two gecko species (Tarentola mauritanica and Hemidactylus turcicus). Using quantitative PCR, it was found that 14/49 (28.57%) of adult Tarentola mauritanica were positive for Leishmania parasites, 13/49 (26.53%) for L. tarentolae and 74/49 (8.16%) for L. infantum. Additionally, coinfection of both parasites was detected in three geckos (3/49, 6.12%). The second gecko species studied, Hemidactylus turcicus, was not positive for Leishmania, possible due to a small sample size. These results reinforce previous studies suggesting that geckos may carry both parasites. Since L. tarentolae has also been detected in dogs, and both Leishmania species are sympatric, it raises questions about the role of reptiles in leishmaniosis cycle and transmission, as well as the reliability of current diagnostic tests in coinfections of closely related parasite species.

microbiology↗

bioRxiv2024

Effects of meglumine antimoniate and allopurinol treatment on the fecal microbiome profile in dogs with leishmaniosis

The combination of meglumine antimoniate and allopurinol is considered one of the most effective treatments for canine leishmaniosis caused by Leishmania infantum. This study investigated the effects of this treatment on the gut microbiome of 10 dogs from Spain, Portugal, and Italy via fecal shotgun metagenomic sequencing over six months. Dogs were sampled at baseline (BL) and at one (M1) and six (M6) months post-treatment. The gut microbiome of Leishmania-infected dogs (BL) is dominated by Prevotella, Collinsella, Bacteroides, and Blautia, with individual variability being the primary determinant of microbiome composition. No significant changes in alpha diversity (Shannon index, gene number) or beta diversity (Bray-Curtis dissimilarity, UniFrac distance) were detected between pre- and post-treatment time points, suggesting that treatment with meglumine antimoniate and allopurinol does not disrupt the gut microbiota. Minor trends in taxonomic shifts were noted, with slight increases in Bifidobacterium pseudocantenulatum, Collinsella tanakaei, and Slackia piriformis after treatment, but these changes were not statistically significant after correction for multiple testing. Linear discriminant analysis and multivariable modeling confirmed that the microbial community structure was resilient to treatment effects. Individual-specific microbiome differences in diversity accounted for 52% of the observed variability, underscoring the personalized nature of the gut microbiota in dogs. Importantly, no adverse microbiome disruptions were detected, even with prolonged allopurinol use. This study highlights the robustness of the canine gut microbiome during antileishmanial therapy and highlights the use of meglumine antimoniate and allopurinol without compromising gut microbial diversity or health. Further studies with larger cohorts are recommended to confirm these findings and explore the functional roles of the gut microbiota in modulating immune responses in Leishmania-infected dogs.

molecular biology↗

bioRxiv2024

Asymmetries in foveal vision

Visual perception is characterized by known asymmetries in the visual field; humans visual sensitivity is higher along the horizontal than the vertical meridian, and along the lower than the upper vertical meridian. These asymmetries decrease with decreasing eccentricity from the periphery to the center of gaze, suggesting that they may be absent in the 1-deg foveola, the retinal region used to explore scenes at high-resolution. Using high-precision eyetracking and gaze-contingent display, allowing for accurate control over the stimulated foveolar location despite the continuous eye motion at fixation, we investigated fine visual discrimination at different isoeccentric locations across the foveola and parafovea. Although the tested foveolar locations were only 0.3 deg away from the center of gaze, we show that, similar to more eccentric locations, humans are more sensitive to stimuli presented along the horizontal than the vertical meridian. Whereas the magnitude of this asymmetry is reduced in the foveola, the magnitude of the vertical meridian asymmetry is comparable but, interestingly, reversed: objects presented slightly above the center of gaze are more easily discerned than when presented at the same eccentricity below the center of gaze. Therefore, far from being uniform, as often assumed, foveolar vision is characterized by perceptual asymmetries. Further, these asymmetries differ not only in magnitude but also in direction compared to those present just [~]4deg away from the center of gaze, resulting in overall different foveal and extrafoveal perceptual fields.

neuroscience↗

bioRxiv2024

Defense mechanisms in Lupinus luteus against Colletotrichum lupini, involving TIR-NBS-LRR protein, hypersensitive response and phenylpropanoid pathways

Lupins are key grain legumes for future crop production, providing highly sustainable protein, essential in the face of global warming, food security challenges, and the need for sustainable agriculture. Despite their potential, lupin crops are frequently devastated by Colletotrichum lupini, a member of the worlds top ten fungal pathogenic genera. In our previous study, we identified LluR1, the first C. lupini resistance gene, in a wild Lupinus luteus accession. Further research was necessary to unravel the defense mechanisms involved. Histological analysis revealed a hypersensitive response against C. lupini, while transcriptome analysis highlighted a complex network of differentially expressed genes, including TIR-NBS-LRR proteins, hypersensitive response, and phenylpropanoid pathways. SNPs were identified that distinguish the protein sequences underlying immunity. These findings, along with orthology in other lupin species, offer valuable insights for developing breeding strategies to enhance C. lupini resistance in lupins, with significant potential impacts on food, feed, and human nutrition.

plant biology↗

bioRxiv2024

How the window of visibility varies around polar angle

Contrast sensitivity, the amount of contrast required to detect or discriminate an object, depends on spatial frequency (SF): The Contrast Sensitivity Function (CSF) peaks at intermediate SFs and drops at lower and higher SFs and is the basis of computational models of visual object recognition. The CSF varies from foveal to peripheral vision, but only a couple studies have assessed changes around polar angle of the visual field. Sensitivity is generally better along the horizontal than the vertical meridian, and better at the lower vertical than the upper vertical meridian, yielding polar angle asymmetries. Here, we investigate CSF attributes at polar angle locations at both group and individual levels, using Hierarchical Bayesian Modeling. This method enables precise estimation of CSF parameters by decomposing the variability of the dataset into multiple levels and analyzing covariance across observers. At the group level, peak contrast sensitivity and corresponding spatial frequency with the highest sensitivity are higher at the horizontal than vertical meridian, and at the lower than upper vertical meridian. At an individual level, CSF attributes (e.g., maximum sensitivity, the most preferred SF) across locations are highly correlated, indicating that although the CSFs differ across locations, the CSF at one location is predictive of the CSF at another location. Within each location, the CSF attributes co-vary, indicating that CSFs across individuals vary in a consistent manner (e.g., as maximum sensitivity increases, wso does the SF at which sensitivity peaks), but more so at the horizontal than the vertical meridian locations. These results show similarities and uncover some critical polar angle differences across locations and individuals, suggesting that the CSF should not be generalized across iso-eccentric locations around the visual field. Our window of visibility varies with polar angle: It is enhanced and more consistent at the horizontal meridian. Author summaryThe contrast sensitivity function (CSF), depicting how our ability to perceive contrast depends on spatial frequency, characterizes our "window of visibility": We can only see objects with contrast and spatial frequency properties encompassed by this function. The CSF is mostly assessed only along the horizontal meridian of the visual field and sometimes averaged across locations, but visual performance varies with polar angle (e.g., we are more sensitive to objects along the horizontal than the vertical meridian). Here, we systematically assess the key attributes of the CSF and show critical differences in the window of visibility across polar angles and individuals. We found that at the horizontal meridian, our overall contrast sensitivity and preferred SF are higher, and CSFs of individual observers co-vary more than at the vertical meridian. This research highlights that this fundamental perceptual measure is not the same and should be assessed around the visual field. Polar angle thus should be a key consideration for applications of the CSF in computational models of vision.

neuroscience↗

bioRxiv2024

Eyes on the past: Gaze stability differs between temporal expectation and temporal attention

Temporal expectation and temporal attention distinctly improve performance and gaze stability, and interact at the behavioral and neural levels. Foreperiod--the interval between the preparatory signal and stimulus onset--facilitates temporal expectation. Preceding foreperiod--the foreperiod in the previous trial--modulates expectation at behavioral and oculomotor levels. Here, we investigated whether preceding foreperiod guides temporal attention. Regardless of the preceding foreperiod, temporal attention improved performance, particularly at early moments,and consistently accelerated gaze stability onset and offset by shifting microsaccade timing. However, only with preceding expected foreperiods, attention inhibited microsaccade rates. Moreover, preceding late foreperiods weakened expectation effects on microsaccade rates, but such a weakening was overridden by attention. Altogether, these findings reveal that the oculomotor systems flexibility does not translate to performance, and suggest that although selection history can be utilized as one of the sources of expectation in subsequent trials, it does not necessarily determine, strengthen, or guide attentional deployment.

neuroscience↗

bioRxiv2024

Temporal attention recruits fronto-cingulate cortex to amplify stimulus representations

The human brain faces significant constraints in its ability to process every item in a sequence of stimuli. Voluntary temporal attention can selectively prioritize a task-relevant item over its temporal competitors to alleviate these constraints. However, it remains unclear when and where in the brain selective temporal attention modulates the visual representation of a prioritized item. Here, we manipulated temporal attention to successive stimuli in a two-target temporal cueing task, while controlling for temporal expectation with fully predictable stimulus timing. We used MEG and time-resolved decoding to track the spatiotemporal evolution of stimulus representations in human observers. We found that temporal attention enhanced the representation of the first target around 250 milliseconds after target onset, in a contiguous region spanning left frontal cortex and cingulate cortex. The results indicate that voluntary temporal attention recruits cortical regions beyond the ventral stream at an intermediate processing stage to amplify the representation of a target stimulus. This routing of stimulus information to anterior brain regions may provide protection from interference in visual cortex by a subsequent stimulus. Thus, voluntary temporal attention may have distinctive neural mechanisms to support specific demands of the sequential processing of stimuli. Significance statementWhen viewing a rapid sequence of visual input, the brain cannot fully process every item. Humans can attend to an item they know will be important to enhance its processing. However, how the brain selects one moment over others is little understood. We found that attending to visual information at a precise moment in time enhances visual representations around 250 ms after an item appears. Unexpectedly, this enhancement occurred not in the visual cortex, but in the left fronto-cingulate cortex. The involvement of frontal rather than posterior cortical regions in representing visual stimuli has not typically been observed for spatial or feature-based attention, suggesting that temporal attention may have specialized neural mechanisms to handle the distinctive demands of sequential processing.

neuroscience↗