Do emotional faces capture attention, and does this depend on awareness? Evidence from the visual probe paradigm

The visual probe (VP) paradigm provides evidence that emotional stimuli attract attention. Such effects have been reported even when stimuli are presented outside of awareness. These findings have shaped the idea that humans possess a processing pathway that detects evolutionarily significant signals independently of awareness. Here, we addressed 2 unresolved questions: First, if emotional stimuli attract attention, is this driven by their affective content, or by low-level image properties (e.g., luminance contrast)? Second, does attentional capture occur under conditions of genuine unawareness? We found that observers preferentially allocated attention to emotional faces under aware viewing conditions. However, this effect was best explained by low-level stimulus properties, rather than emotional content. When stimuli were presented outside of awareness (via continuous flash suppression or masking), we found no evidence that attention was directed toward emotional face stimuli. Finally, observer's awareness of the stimuli (assessed by d') predicted attentional cuing. Our data challenge existing literature: First, we cast doubt on the notion of preferential attention to emotional stimuli in the absence of awareness. Second, we question whether effects revealed by the VP paradigm genuinely reflect emotion-sensitive processes, instead suggesting they can be more parsimoniously explained by low-level variability between stimuli. (PsycINFO Database Record (c) 2019 APA, all rights reserved)

Visual evoked cortical responses and selective dioptic masking with pattern flashes of different spatial frequencies

Human cortical visually evoked responses (VERs) to pairs of stimuli presented in rapid succession were investigated in an attempt to assess the electrophysiological nature of temporal visual processing as a function of the spatial frequency of the stimuli involved. Four stimuli, all of which were of an equal mean luminance level, consisted of a diffuse flash and square checkerboard patterns of three spatial frequencies: 0.5, 1.0, and 4.0 cycles/degree (check-sizes subtending 60, 30, and 7.5 min of arc visual angle). Stimuli were presented both singly and in all 16 possible pairwise combinations with a 40 msec interflash interval interposed between the pairs. Both the psychophysical reports and the VERs to the various stimulus configurations were analyzed in order to test whether the existence of visual information channels selectively tuned to a specific range of spatial frequencies would be revealed in terms of selective masking effects among the various stimulus combinations. Analysis of the VER data was based primarily on the magnitude of variability of the VERs, resulting from variations in the pattern stimulation from the first or second flash. The variability measure indicated the degree to which stimulus pattern processing of one flash of the pair was impaired by the nature of pattern in the preceding or following flash (forward and backward masking effects respectively)

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Temporal Characteristics of Monoptic, Dichoptic and Half-Binocular Collinear Lateral Masking of Contrast Detection

Purpose: The temporal characteristics of dichoptic contrast integration across space in primary visual cortex are relatively unknown. This study investigated the effect of varying interstimulus interval (ISI) and flank duration on contrast detection threshold (CDT) of a sinusoid target under monoptic, dichoptic and half-binocular viewing. Methods: Eleven subjects with normal vision participated for a mean of 25 hours each. In the main experiment, target and flanks were 3 cpd vertical sinusoids with 6 lambda (sigma = 1.5 lambda) center-to-center vertical separation. Flank contrast was normalized to 3X flank CDT. Flanks were presented at 4 durations (67-500ms) and ISIs were presented at 8 durations (0-2500ms) resulting in 0-3000ms stimulus onset asynchronies (SOA). Target presentations were 250ms to dominant eye using a mirror haploscope and septum. Flanks were presented to dominant (monoptic and half-binocular) and non-dominant eyes (dichoptic and half-binocular). Forward masking was used throughout with a 1-FC detection paradigm and 7-level MOCS. Each target CDT was the product of approximately 700 trials. Results: As expected, simultaneous presentation resulted in CDT facilitation (monoptic = 19%± 3.86% (SE), dichoptic = 13.9%± 4.00%, half-binocular = 18.0%± 4.20%). For all viewing conditions, relative facilitation decreased as SOA increased up to 1000ms. Unexpectedly, dichoptic flanks produced significant CDT suppression (p \u3c 0.05) at 500-1000ms SOAs that was maximal at the 1000ms SOA (9.9%± 5.1%). All viewing conditions approached no effect at the longest SOAs (1500-3000ms). Flank duration had a significantly greater contribution to the overall effect than ISI for monoptic (p \u3c 0.01) and half-binocular (p \u3c 0.05) viewing. Discussion: The collinear CDT facilitation produced by intra-ocular and inter-ocular flanks at shorter SOAs is consistent with lateral connections in primary visual cortex. The temporal aspects of longer SOA, dichoptic CDT suppression observed in this study are consistent with prior studies of illusory contour perception. Conclusion: I propose the novel hypothesis that the CDT suppression produced by dichoptic collinear flanks at longer SOAs is due to one-way, contrast adaptation from lateral propagation that produced the effect of a collinear, illusory contour. This hypothesis was supported by the results of a supplemental, orthogonal flank experiment

Temporal Integration of Movement: The Time-Course of Motion Streaks Revealed by Masking

Temporal integration in the visual system causes fast-moving objects to leave oriented ‘motion streaks’ in their wake, which could be used to facilitate motion direction perception. Temporal integration is thought to occur over 100 ms in early cortex, although this has never been tested for motion streaks. Here we compare the ability of fast-moving (‘streaky’) and slow-moving fields of dots to mask briefly flashed gratings either parallel or orthogonal to the motion trajectory. Gratings were presented at various asynchronies relative to motion onset (from to ms) to sample the time-course of the accumulating streaks. Predictions were that masking would be strongest for the fast parallel condition, and would be weak at early asynchronies and strengthen over time as integration rendered the translating dots more streaky and grating-like. The asynchrony where the masking function reached a plateau would correspond to the temporal integration period. As expected, fast-moving dots caused greater masking of parallel gratings than orthogonal gratings, and slow motion produced only modest masking of either grating orientation. Masking strength in the fast, parallel condition increased with time and reached a plateau after 77 ms, providing an estimate of the temporal integration period for mechanisms encoding motion streaks. Interestingly, the greater masking by fast motion of parallel compared with orthogonal gratings first reached significance at 48 ms before motion onset, indicating an effect of backward masking by motion streaks

Motion Extrapolation in the Central Fovea

Neural transmission latency would introduce a spatial lag when an object moves across the visual field, if the latency was not compensated. A visual predictive mechanism has been proposed, which overcomes such spatial lag by extrapolating the position of the moving object forward. However, a forward position shift is often absent if the object abruptly stops moving (motion-termination). A recent “correction-for-extrapolation” hypothesis suggests that the absence of forward shifts is caused by sensory signals representing ‘failed’ predictions. Thus far, this hypothesis has been tested only for extra-foveal retinal locations. We tested this hypothesis using two foveal scotomas: scotoma to dim light and scotoma to blue light. We found that the perceived position of a dim dot is extrapolated into the fovea during motion-termination. Next, we compared the perceived position shifts of a blue versus a green moving dot. As predicted the extrapolation at motion-termination was only found with the blue moving dot. The results provide new evidence for the correction-for-extrapolation hypothesis for the region with highest spatial acuity, the fovea

The role of temporal frequency in continuous flash suppression: A case for a unified framework

In continuous flash suppression (CFS), a rapidly changing Mondrian sequence is presented to one eye in order to suppress a static target presented to the other eye. Targets generally remain suppressed for several seconds at a time, contributing to the widespread use of CFS in studies of unconscious visual processes. Nevertheless, the mechanisms underlying CFS suppression remain unclear, complicating its use and the comprehension of results obtained with the technique. As a starting point, this thesis examined the role of temporal frequency in CFS suppression using carefully controlled stimuli generated by Fourier Transform techniques. A low-level stimulus attribute, the choice of temporal frequency allowed us to evaluate the contributions of early visual processes and test the general assumption that fast update rates drive CFS effectiveness. Three psychophysical studies are described in this thesis, starting with the temporal frequency tuning of CFS (Chapter 2), the relationship between the Mondrian pattern and temporal frequency content (Chapter 3), and finally the role of temporal frequency selectivity in CFS (Chapter 4). Contrary to conventional wisdom, the results showed that the suppression of static targets is largely driven by high spatial frequencies and low temporal frequencies. Faster masker rates, on the other hand, worked best with transient targets. Indicative of early, feature selective processes, these findings are reminiscent of binocular rivalry suppression, demonstrating the possible use of a unified framework

Neural correlates of visual awareness

openL'elaborato si propone di esporre le attuali evidenze riguardanti il modo in cui i contenuti soggettivi di consapevolezza visiva sono codificati a livello neurale. Sebbene i meccanismi neurali della percezione visiva siano ampiamente conosciuti, rimane ancora da chiarire come l'informazione visiva entri a far parte dei contenuti della coscienza. Per identificare i correlati neurali della coscienza (CNC), che rappresentano la minima attività neurale per una specifica esperienza conscia, vengono messe in relazione misure comportamentali di consapevolezza, limitatamente a stimoli presentati in un contesto sperimentale, con i sottostanti meccanismi neurali. Attraverso paradigmi sperimentali come la rivalità binoculare e tecniche di mascheramento visivo è possibile provare ad identificare i CNC contenuto-specifici utilizzando misure neurofisiologiche e tecniche di neuroimaging. Tali tecniche forniscono infatti utili informazioni circa le basi neuroanatomiche e funzionali dell'esperienza sotto esame. Sebbene i meccanismi che sottendono l’attenzione siano spesso associati all'esperienza cosciente, evidenze sperimentali suggeriscono una separazione tra i due processi. Le ricerche sui correlati neurali della consapevolezza visiva indicano come l’attività di una singola area cerebrale non possa essere necessaria e sufficiente a spiegare le qualità dei contenuti coscienti. Sembrerebbe invece essere necessaria una rappresentazione della scena visiva distribuita nella corteccia visiva primaria (V1) e nelle aree visive ventrali con attivazione di regioni temporo-parietali. Misure elettrofisiologiche come la visual awareness negativity (VAN) sono state correlate alla consapevolezza visiva mentre altri indicatori sembrerebbero essere maggiormente legati a processi attentivi. Diversi modelli teorici offrono spiegazioni empiriche sull’emergenza della coscienza dall’attività cerebrale. Nel caso della consapevolezza visiva, alcuni modelli teorici rilevanti sono la teoria dello spazio di lavoro neurale globale, la quale sottolinea la necessità di condivisione dell'informazione tra ampie aree cerebrali e la teoria dell'elaborazione ricorrente che si concentra invece sul feedback proveniente a V1 dalle aree extrastriate. Inoltre, il modello dell’”elaborazione predittiva” descrive la percezione cosciente come il risultato di un processo attivo in cui il cervello crea costantemente previsioni sull’ambiente circostante. Allo stato attuale, la ricerca sui correlati neurali della consapevolezza visiva evidenzia dunque come un network di regioni cerebrali posteriori sia fondamentale per avere esperienze visive coscienti. Inoltre, i segnali di feedback sembrano svolgere un ruolo cruciale, evidenziando le complesse interazioni tra dinamiche neurali e percezione cosciente.The paper aims to present the current evidence regarding how subjective contents of visual awareness are encoded at the neural level. While the neural mechanisms of visual perception are well understood, it remains unclear how visual information becomes part of consciousness. To identify the neural correlates of consciousness (NCC), representing the minimum neural activity for a specific conscious experience, behavioral measures of awareness are related to underlying neural mechanisms, limited to stimuli presented in an experimental context. Through experimental paradigms such as binocular rivalry and visual masking techniques, it is possible to attempt to identify content-specific NCC using neurophysiological measures and neuroimaging techniques. These techniques indeed provide valuable information about the neuroanatomical and functional basis of the examined experience. Although mechanisms underlying attention are often associated with conscious experience, experimental evidence suggests a separation between the two processes. Research on the neural correlates of visual awareness indicates that the activity of a single brain area may not be necessary and sufficient to explain the qualities of conscious contents. Instead, a distributed representation of the visual scene in the primary visual cortex (V1) and ventral visual areas with activation of temporo-parietal regions seems to be necessary. Electrophysiological measures such as Visual Awareness Negativity (VAN) have been correlated with visual awareness, while other indicators appear to be more related to attentional processes. Various theoretical models offer empirical explanations of the emergence of consciousness from brain activity. In the case of visual awareness, some relevant theoretical models include the global neural workspace theory, which emphasizes the need for information sharing among extensive brain areas, and the recurrent processing theory, which focuses on feedback from extrastriate areas to V1. Additionally, the predictive processing model describes conscious perception as the result of an active process in which the brain constantly generates predictions about the surrounding environment. Currently, research on the neural correlates of visual awareness highlights the importance of a network of posterior brain regions for conscious visual experiences. Furthermore, feedback signals appear to play a crucial role, highlighting the complex interactions between neural dynamics and conscious perception

Perceptual stability during saccadic eye movements

Humans and other primates perform multiple fast eye movements per second in order to redirect gaze within the visual field. These so called saccades challenge visual perception: During the movement phases the projection of the outside world sweeps rapidly across the photoreceptors altering the retinal positions of objects that are otherwise stable in the environment. Despite this ever-changing sensory input, the brain creates the percept of a continuous, stable visual world. Currently, it is assumed that this perceptual stability is achieved by the synergistic interplay of multiple mechanisms, for example, a reduction of the sensitivity of the visual system around the time of the eye movement ('saccadic suppression') as well as transient reorganizations in the neuronal representations of space ('remapping'). This thesis comprises six studies on trans-saccadic perceptual stability

Engineering data compendium. Human perception and performance. User's guide

The concept underlying the Engineering Data Compendium was the product of a research and development program (Integrated Perceptual Information for Designers project) aimed at facilitating the application of basic research findings in human performance to the design and military crew systems. The principal objective was to develop a workable strategy for: (1) identifying and distilling information of potential value to system design from the existing research literature, and (2) presenting this technical information in a way that would aid its accessibility, interpretability, and applicability by systems designers. The present four volumes of the Engineering Data Compendium represent the first implementation of this strategy. This is the first volume, the User's Guide, containing a description of the program and instructions for its use