scholarly journals Common spatiotemporal processing of visual features shapes object representation

2018 ◽  
Author(s):  
Paolo Papale ◽  
Monica Betta ◽  
Giacomo Handjaras ◽  
Giulia Malfatti ◽  
Luca Cecchetti ◽  
...  
Keyword(s):  
Object Representation ◽  
Temporal Dynamics ◽  
Medial Axis ◽  
Human Subjects ◽  
Physical World ◽  
Stimulus Onset ◽  
Low Level ◽  
Semantic Categories ◽  
Spatial Frequencies ◽  
Feature Processing

AbstractBiological vision relies on representations of the physical world at different levels of complexity. Relevant features span from simple low-level properties, as contrast and spatial frequencies, to object-based attributes, as shape and category. However, how these features are integrated into coherent percepts is still debated. Moreover, these dimensions often share common biases: for instance, stimuli from the same category (e.g., tools) may have similar shapes. Here, using magnetoencephalography, we revealed the temporal dynamics of feature processing in human subjects attending to pictures of items pertaining to different semantic categories. By employing Relative Weights Analysis, we mitigated collinearity between model-based descriptions of stimuli and showed that low-level properties (contrast and spatial frequencies), shape (medial-axis) and category are represented within the same spatial locations early in time: 100-150ms after stimulus onset. This fast and overlapping processing may result from independent parallel computations, with categorical representation emerging later than the onset of low-level feature processing, yet before shape coding. Categorical information is represented both before and after shape also suggesting a role for this feature in the refinement of categorical matching.

scholarly journals The rhythms of predictive coding: pre-stimulus phase modulates the influence of shape perception on luminance judgments

2016 ◽  
Author(s):  
Biao Han ◽  
Rufin VanRullen
Keyword(s):  
Temporal Dynamics ◽  
Human Subjects ◽  
Predictive Coding ◽  
Shape Perception ◽  
Low Level ◽  
3D Shape ◽  
Coding Efficiency ◽  
Spatial Response ◽  
Left And Right ◽  
High Level

AbstractPredictive coding is an influential model emphasizing interactions between feedforward and feedback signals. Here, we investigated its temporal dynamics. Two gray disks with different versions of the same stimulus, one enabling predictive feedback (a 3D-shape) and one impeding it (random-lines), were simultaneously presented on the left and right of fixation. Human subjects judged the luminance of the two disks while EEG was recorded. Independently of the spatial response (left/right), we found that the choice of 3D-shape or random-lines as the brighter disk (our measure of post-stimulus predictive coding efficiency on each trial) fluctuated along with the pre-stimulus phase of two spontaneous oscillations: a ~5Hz oscillation in contralateral frontal electrodes and a ~16Hz oscillation in contralateral occipital electrodes. This pattern of results demonstrates that predictive coding is a rhythmic process, and suggests that it could take advantage of faster oscillations in low-level areas and slower oscillations in high-level areas.

scholarly journals Interactions between Auditory and Visual Semantic Stimulus Classes: Evidence for Common Processing Networks for Speech and Body Actions

2011 ◽  
Vol 23 (9) ◽  
pp. 2291-2308 ◽  
Author(s):  
Georg F. Meyer ◽  
Mark Greenlee ◽  
Sophie Wuerger
Keyword(s):  
Human Performance ◽  
Inferior Frontal Gyrus ◽  
Audiovisual Integration ◽  
Visual Signals ◽  
Bold Response ◽  
Activation Patterns ◽  
Semantic Congruency ◽  
Low Level ◽  
Semantic Categories ◽  
Premotor Areas

Incongruencies between auditory and visual signals negatively affect human performance and cause selective activation in neuroimaging studies; therefore, they are increasingly used to probe audiovisual integration mechanisms. An open question is whether the increased BOLD response reflects computational demands in integrating mismatching low-level signals or reflects simultaneous unimodal conceptual representations of the competing signals. To address this question, we explore the effect of semantic congruency within and across three signal categories (speech, body actions, and unfamiliar patterns) for signals with matched low-level statistics. In a localizer experiment, unimodal (auditory and visual) and bimodal stimuli were used to identify ROIs. All three semantic categories cause overlapping activation patterns. We find no evidence for areas that show greater BOLD response to bimodal stimuli than predicted by the sum of the two unimodal responses. Conjunction analysis of the unimodal responses in each category identifies a network including posterior temporal, inferior frontal, and premotor areas. Semantic congruency effects are measured in the main experiment. We find that incongruent combinations of two meaningful stimuli (speech and body actions) but not combinations of meaningful with meaningless stimuli lead to increased BOLD response in the posterior STS (pSTS) bilaterally, the left SMA, the inferior frontal gyrus, the inferior parietal lobule, and the anterior insula. These interactions are not seen in premotor areas. Our findings are consistent with the hypothesis that pSTS and frontal areas form a recognition network that combines sensory categorical representations (in pSTS) with action hypothesis generation in inferior frontal gyrus/premotor areas. We argue that the same neural networks process speech and body actions.

Temporal Dynamics of Shape Analysis in Macaque Visual Area V2

2004 ◽  
Vol 92 (5) ◽  
pp. 3030-3042 ◽  
Author(s):  
Jay Hegdé ◽  
David C. Van Essen
Keyword(s):  
Cortical Neurons ◽  
Time Course ◽  
Temporal Dynamics ◽  
Visual Stimulation ◽  
Signal To Noise Ratio ◽  
Stimulus Onset ◽  
Visual Area ◽  
Response Modulation ◽  
Population Response ◽  
Area V2

The firing rate of visual cortical neurons typically changes substantially during a sustained visual stimulus. To assess whether, and to what extent, the information about shape conveyed by neurons in visual area V2 changes over the course of the response, we recorded the responses of V2 neurons in awake, fixating monkeys while presenting a diverse set of static shape stimuli within the classical receptive field. We analyzed the time course of various measures of responsiveness and stimulus-related response modulation at the level of individual cells and of the population. For a majority of V2 cells, the response modulation was maximal during the initial transient response (40–80 ms after stimulus onset). During the same period, the population response was relatively correlated, in that V2 cells tended to respond similarly to specific subsets of stimuli. Over the ensuing 80–100 ms, the signal-to-noise ratio of individual cells generally declined, but to a lesser degree than the evoked-response rate during the corresponding time bins, and the response profiles became decorrelated for many individual cells. Concomitantly, the population response became substantially decorrelated. Our results indicate that the information about stimulus shape evolves dynamically and relatively rapidly in V2 during static visual stimulation in ways that may contribute to form discrimination.

scholarly journals Repeated Low-Level Blast Exposure: A Descriptive Human Subjects Study

2016 ◽  
Vol 181 (5S) ◽  
pp. 28-39 ◽  
Author(s):  
Walter Carr ◽  
James R. Stone ◽  
Tim Walilko ◽  
Lee Ann Young ◽  
Tianlu Li Snook ◽  
...  
Keyword(s):  
Human Subjects ◽  
Low Level ◽  
Blast Exposure

Foveal Attention Modulates Responses to Peripheral Stimuli

2000 ◽  
Vol 83 (4) ◽  
pp. 2443-2452 ◽  
Author(s):  
Simo Vanni ◽  
Kimmo Uutela
Keyword(s):  
Visual Field ◽  
Target Location ◽  
Peripheral Vision ◽  
Human Subjects ◽  
Stimulus Onset ◽  
Visual Object ◽  
Frontal Eye Field ◽  
L1 Norm ◽  
Luminance Stimulus ◽  
The Right

When attending to a visual object, peripheral stimuli must be monitored for appropriate redirection of attention and gaze. Earlier work has revealed precentral and posterior parietal activation when attention has been directed to peripheral vision. We wanted to find out whether similar cortical areas are active when stimuli are presented in nonattended regions of the visual field. The timing and distribution of neuromagnetic responses to a peripheral luminance stimulus were studied in human subjects with and without attention to fixation. Cortical current distribution was analyzed with a minimum L1-norm estimate. Attention enhanced responses 100–160 ms after the stimulus onset in the right precentral cortex, close to the known location of the right frontal eye field. In subjects whose right precentral region was not distinctly active before 160 ms, focused attention commonly enhanced right inferior parietal responses between 180 and 240 ms, whereas in the subjects with clear earlier precentral response no parietal enhancement was detected. In control studies both attended and nonattended stimuli in the peripheral visual field evoked the right precentral response, whereas during auditory attention the visual stimuli failed to evoke such response. These results show that during focused visual attention the right precentral cortex is sensitive to stimuli in all parts of the visual field. A rapid response suggests bypassing of elaborate analysis of stimulus features, possibly to encode target location for a saccade or redirection of attention. In addition, load for frontal and parietal nodi of the attentional network seem to vary between individuals.

scholarly journals Rapid orienting of spatial attention toward and away from aggressive voices

2017 ◽  
Author(s):  
Nicolas Burra ◽  
Dirk Kerzel ◽  
David Munoz ◽  
Didier Grandjean ◽  
Leonardo Ceravolo
Keyword(s):  
Spatial Attention ◽  
Auditory Processing ◽  
Temporal Dynamics ◽  
Detection System ◽  
Stimulus Onset ◽  
Event Related Potential ◽  
Auditory Modality ◽  
Attentional Processing ◽  
Auditory Spatial Attention ◽  
Vocal Signals

Salient vocalizations, especially aggressive voices, are believed to attract attention due to an automatic threat detection system. However, studies assessing the temporal dynamics of auditory spatial attention to aggressive voices are missing. Using event-related potential markers of auditory spatial attention (N2ac and LPCpc), we show that attentional processing of threatening vocal signals is enhanced at two different stages of auditory processing. As early as 200 ms post stimulus onset, attentional orienting/engagement is enhanced for threatening as compared to happy vocal signals. Subsequently, as early as 400 ms post stimulus onset, the reorienting of auditory attention to the center of the screen (or disengagement from the target) is enhanced. This latter effect is consistent with the need to optimize perception by balancing the intake of stimulation from left and right auditory space. Our results extend the scope of theories from the visual to the auditory modality by showing that threatening stimuli also bias early spatial attention in the auditory modality. Although not the focus of the present work, we observed that the attentional enhancement was more pronounced in female than male participants.

scholarly journals The Temporal Dynamics of Object Processing in Visual Cortex during the Transition from Distributed to Focused Spatial Attention

2011 ◽  
Vol 23 (12) ◽  
pp. 4094-4105 ◽  
Author(s):  
Chien-Te Wu ◽  
Melissa E. Libertus ◽  
Karen L. Meyerhoff ◽  
Marty G. Woldorff
Keyword(s):  
Visual Cortex ◽  
Spatial Attention ◽  
Cognitive Neuroscience ◽  
Visual Processing ◽  
Object Representation ◽  
Temporal Dynamics ◽  
Brain Activity ◽  
Object Processing ◽  
Electrical Brain Activity

Several major cognitive neuroscience models have posited that focal spatial attention is required to integrate different features of an object to form a coherent perception of it within a complex visual scene. Although many behavioral studies have supported this view, some have suggested that complex perceptual discrimination can be performed even with substantially reduced focal spatial attention, calling into question the complexity of object representation that can be achieved without focused spatial attention. In the present study, we took a cognitive neuroscience approach to this problem by recording cognition-related brain activity both to help resolve the questions about the role of focal spatial attention in object categorization processes and to investigate the underlying neural mechanisms, focusing particularly on the temporal cascade of these attentional and perceptual processes in visual cortex. More specifically, we recorded electrical brain activity in humans engaged in a specially designed cued visual search paradigm to probe the object-related visual processing before and during the transition from distributed to focal spatial attention. The onset times of the color popout cueing information, indicating where within an object array the subject was to shift attention, was parametrically varied relative to the presentation of the array (i.e., either occurring simultaneously or being delayed by 50 or 100 msec). The electrophysiological results demonstrate that some levels of object-specific representation can be formed in parallel for multiple items across the visual field under spatially distributed attention, before focal spatial attention is allocated to any of them. The object discrimination process appears to be subsequently amplified as soon as focal spatial attention is directed to a specific location and object. This set of novel neurophysiological findings thus provides important new insights on fundamental issues that have been long-debated in cognitive neuroscience concerning both object-related processing and the role of attention.

The co-occurrence of multisensory facilitation and cross-modal conflict in the human brain

2011 ◽  
Vol 106 (6) ◽  
pp. 2896-2909 ◽  
Author(s):  
Andreea Oliviana Diaconescu ◽  
Claude Alain ◽  
Anthony Randal McIntosh
Keyword(s):  
Multisensory Processing ◽  
Semantic Relatedness ◽  
Semantic Category ◽  
Brain Regions ◽  
Stimulus Onset ◽  
Semantic Categories ◽  
Task Instructions ◽  
Specific Object ◽  
Posterior Parietal ◽  
Multisensory Processes

Perceptual objects often comprise a visual and auditory signature that arrives simultaneously through distinct sensory channels, and cross-modal features are linked by virtue of being attributed to a specific object. Continued exposure to cross-modal events sets up expectations about what a given object most likely “sounds” like, and vice versa, thereby facilitating object detection and recognition. The binding of familiar auditory and visual signatures is referred to as semantic, multisensory integration. Whereas integration of semantically related cross-modal features is behaviorally advantageous, situations of sensory dominance of one modality at the expense of another impair performance. In the present study, magnetoencephalography recordings of semantically related cross-modal and unimodal stimuli captured the spatiotemporal patterns underlying multisensory processing at multiple stages. At early stages, 100 ms after stimulus onset, posterior parietal brain regions responded preferentially to cross-modal stimuli irrespective of task instructions or the degree of semantic relatedness between the auditory and visual components. As participants were required to classify cross-modal stimuli into semantic categories, activity in superior temporal and posterior cingulate cortices increased between 200 and 400 ms. As task instructions changed to incorporate cross-modal conflict, a process whereby auditory and visual components of cross-modal stimuli were compared to estimate their degree of congruence, multisensory processes were captured in parahippocampal, dorsomedial, and orbitofrontal cortices 100 and 400 ms after stimulus onset. Our results suggest that multisensory facilitation is associated with posterior parietal activity as early as 100 ms after stimulus onset. However, as participants are required to evaluate cross-modal stimuli based on their semantic category or their degree of congruence, multisensory processes extend in cingulate, temporal, and prefrontal cortices.

scholarly journals Space-temporal Dynamics of Agriculture in the Primavera Municipality, Pará State, Brazil: Subsidies for Agroecological Transition

2020 ◽  
Vol 8 (2) ◽  
pp. 518
Author(s):  
Caio Cezar Ferreira de Souza ◽  
Marcos Antônio Souza dos Santos ◽  
Fabrício Khoury Rebello ◽  
Cyntia Meireles Martins ◽  
Maria Lúcia Bahia Lopes ◽  
...  
Keyword(s):  
Agricultural Production ◽  
Agricultural Sector ◽  
Temporal Dynamics ◽  
Production Systems ◽  
Secondary Data ◽  
Land Occupation ◽  
Low Level ◽  
Human Needs ◽  
Agroecological Transition ◽  
Mining Projects

The exploitation of natural resources to meet human needs for, among other reasons, the advancement of agriculture, livestock, and mining projects, causes changes in environmental systems in time and space. The research objective of this study is to evaluate the space-temporal dynamics of agriculture in the Primavera municipality, located in the Pará Northeast, from 1980 to 2018, and to offer subsidies for the agroecological transition of current agricultural production systems. The methodology is based on the analysis of land use and land cover maps, in three different periods (1984, 2008 and 2018), by using image processing from the LANDSAT (1984 and 2008) and Sentinel (2018) satellites. Agricultural sector characterization was also analyzed, by using secondary data on socioeconomic and productivity variables. The results show that, even after the setup of a large mining enterprise in the Primavera municipality, the agricultural sector did not show major changes in terms of land occupation, increasing from 23.3% (2008) to 29.3% (2018). In addition, when analyzing the agricultural sector, the technology level was found to be at a low level, with little use of chemical inputs and machines. Agricultural diversification was also found to be at a low level, with the cultivation of five crops, predominantly. It is necessary to seek alternatives to improve agricultural production, which can be made viable through the incorporation of sustainable production systems, based on agroecological principles.

scholarly journals The medial axis as a robust model of object representation

2016 ◽  
Vol 16 (12) ◽  
pp. 169 ◽  
Author(s):  
Vladislav Ayzenberg ◽  
Sami Yousif ◽  
Stella Lourenco
Keyword(s):  
Object Representation ◽  
Medial Axis ◽  
Robust Model
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