Biology subjects

Oliva, A.

Publications and source records attributed to Oliva, A..

5 recordsLinked to original sources

bioRxiv2018

Reliability and Generalizability of Similarity-Based Fusion of MEG and fMRI Data in Human Ventral and Dorsal Visual Streams

To build a representation of what we see, the human brain recruits regions throughout the visual cortex in cascading sequence. Recently, an approach was proposed to evaluate the dynamics of visual perception in high spatiotemporal resolution at the scale of the whole brain. This method combined functional magnetic resonance imaging (fMRI) data with magnetoencephalography (MEG) data using representational similarity analysis and revealed a hierarchical progression from primary visual cortex through the dorsal and ventral streams. To assess the replicability of this method, here we present results of a visual recognition neuro-imaging fusion experiment, and compare them within and across experimental settings. We evaluated the reliability of this method by assessing the consistency of the results under similar test conditions, showing high agreement within participants. We then generalized these results to a separate group of individuals and visual input by comparing them to the fMRI-MEG fusion data of Cichy et al (2016), revealing a highly similar temporal progression recruiting both the dorsal and ventral streams. Together these results are a testament to the reproducibility of the fMRI-MEG fusion approach and allows for the interpretation of these spatiotemporal dynamic in a broader context.

neuroscience↗

bioRxiv2018

The Perceptual Neural Trace of Memorable Unseen Scenes

Some scenes are more memorable than others: they cement in minds with consistencies across observers and time scales. While memory mechanisms are traditionally associated with the end stages of perception, recent behavioral studies suggest that the features driving these memorability effects are extracted early on, and in an automatic fashion. This raises the question: is the neural signal of memorability detectable during early perceptual encoding phases of visual processing? Using the high temporal resolution of magnetoencephalography (MEG), during a rapid serial visual presentation (RSVP) task, we traced the neural temporal signature of memorability across the brain. We found an early and prolonged memorability related signal recruiting a network of regions in both dorsal and ventral streams, detected outside of the constraints of subjective awareness. This enhanced encoding could be the key to successful storage and recognition.

neuroscience↗

bioRxiv2018

Accounting for ambiguity in ancestral sequence reconstruction

The reconstruction of ancestral genetic sequences from the analysis of contemporaneous data is a powerful tool to improve our understanding of molecular evolution. Various statistical criteria defined in a phylogenetic framework can be used to infer nucleotide, aminoa-cid or codon states at internal nodes of the tree, for every position along the sequence. These criteria generally select the state that maximises (or minimises) a given criterion. Although it is perfectly sensible from a statistical perspective, that strategy fails to convey useful information about the level of uncertainty associated to the inference. The present study introduces a new criterion for ancestral nucleotide reconstruction that selects a single state whenever the signal conveyed by the data is strong, and a combination of multiple states otherwise. Simulations demonstrate the benefit of this approach with a substantial increase in the accuracy of ancestral sequence reconstruction without significantly compromising on the precision of the solutions returned.

evolutionary biology↗

bioRxiv2017

Image Memorability In The Eye Of The Beholder: Tracking The Decay Of Visual Scene Representations

Some images stick in your mind for days or even years, while others seem to vanish quickly from memory. We tested whether differences in image memorability 1) are already evident immediately after encoding, 2) produce different rates of forgetting, and 3) whether the retrieval of images with different memorability scores affords differential degrees of cognitive load, mirrored by graded pupillary and blink rate responses. We monitored participants eye activity while they viewed a sequence of >1200 images in a repetition detection paradigm. 240 target images from 3 non-overlapping memorability classes were repeated at 4 different lags. Overall, performance decreased log-linearly with time. Differences in memorability were already visible at the shortest lag (~ 20 sec) and became more pronounced as time passed on. The rate of forgetting was steepest for low memorable images. We found that pupils dilated significantly more to correctly identified targets than correctly rejected distractors. Importantly, this \"pupil old/new effect\" increased with increasing number of lags and decreasing image memorability. A similar modulation of blink rates corroborated these findings. These results suggest that during memory retrieval of scenes, image inherent characteristics pose differential degrees of cognitive load on observers as seen in their eyes.

neuroscience↗

bioRxiv2017

Visual memories are stored along a compressed timeline

In continuous recognition the recency effect manifests as a decrease in accuracy and a sublinear increase in response time (RT) with the lag of a repeated stimulus. The recency effect could result from the gradual weakening of mnemonic traces. Alternatively, the recency effect could result from a search through a compressed timeline of recent experience. These two hypotheses make very different predictions about the shape of response time distributions. Using highly-memorable pictures to mitigate changes in accuracy enabled a detailed examination of the effect of recency on retrieval dynamics. The recency at which pictures were repeated ranged over two orders of magnitude across three experiments. Analysis of the RT distributions showed that the time at which memories became accessible changed with the recency of the probe, as predicted by a serial search model suggesting that visual memories can be accessed by sequentially scanning along a compressed representation of the past.

animal behavior and cognition↗