Eye and head movements in visual search in the extended field of view.

In natural environments, head movements are required to search for objects outside the field of view (FoV). Here we investigate the power of a salient target in an extended visual search array to facilitate faster detection once this item comes into the FoV by a head movement. We conducted two virtual reality experiments using spatially clustered sets of stimuli to observe target detection and head and eye movements during visual search. Participants completed search tasks with three conditions: (1) target in the initial FoV, (2) head movement needed to bring the target into the FoV, (3) same as condition 2 but the periphery was initially hidden and appeared after the head movement had brought the location of the target set into the FoV. We measured search time until participants found a more salient (O) or less salient (T) target among distractors (L). On average O's were found faster than T's. Gaze analysis showed that saliency facilitation occurred due to the target guiding the search only if it was within the initial FoV. When targets required a head movement to enter the FoV, participants followed the same search strategy as in trials without a visible target in the periphery. Moreover, faster search times for salient targets were only caused by the time required to find the target once the target set was reached. This suggests that the effect of stimulus saliency differs between visual search on fixed displays and when we are actively searching through an extended visual field.

Eyeball translations affect saccadic eye movements beyond brainstem control.

Vision requires that we rotate our eyes frequently to look at informative structures in the scene. Eye movements are planned by the brain but their execution depends on the mechanical properties of the oculomotor plant, that is, the arrangement of eyeball position, muscle insertions, and pulley locations. Therefore, the biomechanics of rotations is sensitive to eyeball translation because it changes muscle levers. Eyeball translations are little researched as they are difficult to measure with conventional techniques. Here, we investigated the effects of eyeball translation on the coordination of eyeball rotation by high-speed MRI recordings of saccadic eye movements during blinks, which are known to produce strong translations. We found that saccades during blinks massively overshoot their targets and that these overshoots occur in a transient fashion such that the gaze is back on target at the time the blink ends. These dynamic overshoots were tightly coupled to the eyeball translation, both in time and in size. Saccades made without blinks were also accompanied by small amounts of transient eyeball retraction, the size of which scaled with saccade amplitude. These findings demonstrate a complex combination of rotation and translation of the eye. The mechanical consequences of eyeball translation on oculomotor control should be considered along with the neural implementation in the brainstem to understand the generation of eye movements and their disorders.NEW & NOTEWORTHY We found that saccades during blinks can massively overshoot their target when the eyeball is retracted. Our data imply that the overshoots are not part of the saccade plan prepared in the brainstem, but instead a consequence of the altered biomechanics resulting from concurrent eyeball translation and rotation. To our best knowledge, this is the first direct observation of dynamic properties of the oculomotor plant altering the execution of rotational eye movements.

Timing and kinematics of horizontal within-blink saccades measured by EOG.

Eyeblinks are the brief closures of the lid. They are accompanied by a cocontraction of the eye muscles that temporarily pulls the whole eyeball back into its socket. When blinks occur together with execution of saccadic gaze shifts, they interfere with the saccadic premotor circuit, causing these within-blink saccades to be slower than normal and also time-locked to blinks. To analyze the trajectory of within-blink saccades, subtraction of the entangled blink-related eye movement is required. Here we propose a combination of principal component analysis (PCA) and a regression model to subtract the blink-related component of the eye movement based on the respective blink metrics. We used electrooculography (EOG) to measure eye and lid movements of 12 participants who performed saccades with and without blinks. We found that within-blink saccades are slower than without-blink saccades and are tightly coupled in time to blink onset. Surprisingly, in some participants we observed large dynamic overshoots of up to 15° for saccades of only 5° amplitude. The finding of dynamic overshoots was independently confirmed by dynamic MRI for two of the participants and challenges the current view that within-blink saccades are programmed as slow, but straight, saccades. We hypothesize that the dynamic overshoots could be attributed to inhibition of omnipause neurons during blinks, the simultaneous cocontraction of extraocular muscles, or a combination of both.NEW & NOTEWORTHY This study observed that people make large dynamic overshoots when making a saccadic eye movement within a blink but their eyes are back on target by the time the eyelids are open. We used electrooculography (EOG) to measure eye movements even when the lid is down and introduced a novel procedure to subtract blink-related EOG components. These findings challenge the current view that within-blink saccades are programmed as slow but straight saccades.

Effect of sustained selective attention on steady-state visual evoked potentials.

Visual-spatial selective attention enhances the processing of task-relevant visual events while suppressing the processing of irrelevant ones. In this study, we employed a frequency-tagging paradigm to investigate how sustained visual-spatial attention modulates the first harmonic and second harmonic steady-state visual evoked potentials (SSVEPs). Unlike previous studies, that investigated stimulation durations of 10 s or less, we tested a 30-s period. SSVEPs were elicited by simultaneously presenting to the right and left visual hemifields two pattern reversal checkerboard stimuli modulating at 7.14 Hz and 11.11 Hz. Participants were cued to selectively attend to one visual hemifield while ignoring the other. Behavioral results indicated that participants selectively attended to the cued visual hemifield. When participants attended to the visual stimuli, there were larger second harmonic SSVEPs but no attentional modulation of first harmonics. The results are consistent with the proposal that neural populations underlying first, and second harmonics have distinct functional roles, i.e., first harmonics' mechanisms preserve stimulus properties and are resistant to attentional gain, whereas second harmonics mediate attentional modulation. This interpretation is supported by a gain control theory of selective attention.

Real-Time MRI Reveals Unique Insight into the Full Kinematics of Eye Movements.

Our eyes are constantly in motion and the various kinds of eye movements are closely linked to many aspects of human cognitive processing. Measuring all possible eye movements unobtrusively is not achievable with current methods. Video-based eye-trackers only measure rotational but not translational motion of the eye, require a calibration process relying on the participant's self-report of accurate fixation, and do not work if vision of the eyeball is blocked. Scleral search coils attach physical weight on the eyeball and also do not measure translation. Here, we describe a novel and fully automated method to use real-time magnetic resonance imaging (MRI) for eye tracking. We achieved a temporal resolution sufficient to measure eye rotations and translations as short as those that occur within a blink and behind a closed eyelid. To demonstrate this method, we measured the full extent of the blink-related eye movement for two individuals, suggesting that the eye approaches a holding position during lid closure and can move by as much as 35° in rotation and 2 mm in translation. We also investigated the coordination of gaze shifts with blinks. We found that the gaze shift is tightly coupled in time to the translational blink movement and that blinks can induce significant temporal shifts of the gaze trajectory between left and right eye. Our MR-based Eye Tracking (MREyeTrack) method allows measurement of eye movements in terms of both translation and rotation and enables new opportunities for studying ocular motility and its disorders.

Saccadic suppression in schizophrenia.

About 40% of schizophrenia patients report discrete visual disturbances which could occur if saccadic suppression, the decrease of visual sensitivity around saccade onset, is impaired. Two mechanisms contribute to saccadic suppression: efference copy processing and backwards masking. Both are reportedly altered in schizophrenia. However, saccadic suppression has not been investigated in schizophrenia. 17 schizophrenia patients and 18 healthy controls performed a saccadic suppression task using a Gabor stimulus with individually adjusted contrast, which was presented within an interval 300 ms around saccade onset. Visual disturbance scores were higher in patients than controls, but saccadic suppression strength and time course were similar in both groups with lower saccadic suppression rates being similarly related to smaller saccade amplitudes. Saccade amplitudes in the saccadic suppression task were reduced in patients, in contrast to unaltered amplitudes during a saccade control task. Notably, smaller saccade amplitudes were related to higher visual disturbances scores in patients. Saccadic suppression performance was unrelated to symptom expression and antipsychotic medication. Unaltered saccadic suppression in patients suggests sufficiently intact efference copy processing and backward masking as required for this task. Instead, visual disturbances in patients may be related to restricted saccadic amplitudes arising from cognitive load while completing a task.

A Comparison of Eye Tracking Latencies Among Several Commercial Head-Mounted Displays.

A number of virtual reality head-mounted displays (HMDs) with integrated eye trackers have recently become commercially available. If their eye tracking latency is low and reliable enough for gaze-contingent rendering, this may open up many interesting opportunities for researchers. We measured eye tracking latencies for the Fove-0, the Varjo VR-1, and the High Tech Computer Corporation (HTC) Vive Pro Eye using simultaneous electrooculography measurements. We determined the time from the occurrence of an eye position change to its availability as a data sample from the eye tracker (delay) and the time from an eye position change to the earliest possible change of the display content (latency). For each test and each device, participants performed 60 saccades between two targets 20° of visual angle apart. The targets were continuously visible in the HMD, and the saccades were instructed by an auditory cue. Data collection and eye tracking calibration were done using the recommended scripts for each device in Unity3D. The Vive Pro Eye was recorded twice, once using the SteamVR SDK and once using the Tobii XR SDK. Our results show clear differences between the HMDs. Delays ranged from 15 ms to 52 ms, and the latencies ranged from 45 ms to 81 ms. The Fove-0 appears to be the fastest device and best suited for gaze-contingent rendering.

Adaptation to geometrically skewed moving images: An asymmetrical effect on the double-drift illusion.

Progressive addition lenses introduce distortions in the peripheral visual field that alter both form and motion perception. Here we seek to understand how our peripheral visual field adapts to complex distortions. The adaptation was induced across the visual field by geometrically skewed image sequences, and aftereffects were measured via changes in perception of the double-drift illusion. The double-drift or curveball stimulus contains both local and object motion. Therefore, the aftereffects induced by geometrical distortions might be indicative of how this adaptation interacts with the local and object motion signals. In the absence of the local motion components, the adaptation to skewness modified the perceived trajectory of object motion in the opposite direction of the adaptation stimulus skew. This effect demonstrates that the environment can also tune perceived object trajectories. Testing with the full double-drift stimulus, adaptation to a skew in the opposite direction to the local motion component induced a change in perception, reducing the illusion magnitude (when the stimulus was presented on the right side of the screen. A non-statistically significant shift, when stimuli were on the left side). However, adaptation to the other orientation resulted in no change in the strength of the double-drift illusion (for both stimuli locations). Thus, it seems that the adaptor's orientation and the motion statistics of the stimulus jointly define the perception of the measured aftereffect. In conclusion, not only size, contrast or drifting speed affects the double-drift illusion, but also adaptation to image distortions.

Fixation related shifts of perceptual localization counter to saccade direction.

Perisaccadic compression of the perceived location of flashed visual stimuli toward a saccade target occurs from about 50 ms before a saccade. Here we show that between 150 and 80 ms before a saccade, perceived locations are shifted toward the fixation point. To establish the cause of the "reverse" presaccadic perceptual distortion, participants completed several versions of a saccade task. After a cue to saccade, a probe bar stimulus was briefly presented within the saccade trajectory. In Experiment 1 participants made (a) overlap saccades with immediate return saccades, (b) overlap saccades, and (c) step saccades. In Experiment 2 participants made gap saccades in complete darkness. In Experiment 3 participants maintained fixation with the probe stimuli masked at various interstimulus intervals. Participants indicated the bar's location using a mouse cursor. In all conditions in Experiment 1 presaccadic compression was preceded by compression toward the initial fixation. In Experiment 2, saccadic compression was maintained but the preceding countercompression was not observed. Stimuli masked at fixation were not compressed. This suggests the two opposing compression effects are related to the act of executing an eye movement. They are also not caused by the requirement to make two sequential saccades ending at the initial fixation location and are not caused by continuous presence of the fixation markers. We propose that countercompression is related to fixation activity and is part of the sequence of motor preparations to execute a cued saccade.

Intact prioritisation of unconscious face processing in schizophrenia.

INTRODUCTION: Faces provide a rich source of social information, crucial for the successful navigation of daily social interactions. People with schizophrenia suffer a wide range of social-cognitive deficits, including abnormalities in face perception. However, to date, studies of face perception in schizophrenia have primarily employed tasks that require patients to make judgements about the faces. It is, thus, unclear whether the reported deficits reflect an impairment in encoding visual face information, or biased social-cognitive evaluative processes. METHODS: We assess the integrity of early unconscious face processing in 21 out-patients diagnosed with Schizophrenia or Schizoaffective Disorder (15M/6F) and 21 healthy controls (14M/7F). In order to control for any direct influence of higher order cognitive processes, we use a behavioural paradigm known as breaking continuous flash suppression (b-CFS), where participants simply respond to the presence and location of a face. In healthy adults, this method has previously been used to show that upright faces gain rapid and privileged access to conscious awareness over inverted faces and other inanimate objects. RESULTS: Here, we report similar effects in patients, suggesting that the early unconscious stages of face processing are intact in schizophrenia. CONCLUSION: Our data indicate that face processing deficits reported in the literature must manifest at a conscious stage of processing, where the influence of mentalizing or attribution biases might play a role.

Two sources of bias explain errors in facial age estimation.

Accurate age estimates underpin our everyday social interactions, the provision of age-restricted services and police investigations. Previous work suggests that these judgements are error-prone, but the processes giving rise to these errors are not understood. Here, we present the first systematic test of bias in age estimation using a large database of standardized passport images of heterogeneous ages (n = 3948). In three experiments, we tested a range of perceiver age groups (n = 84), and found average age estimation error to be approximately 8 years. We show that this error can be attributed to two separable sources of bias. First, and accounting for the vast majority of variance, our results show an assimilative serial dependency whereby estimates are systematically biased towards the age of the preceding face. Second, younger faces are generally perceived to be older than they are, and older faces to be younger. In combination, these biases account for around 95% of variance in age estimates. We conclude that perception of age is modulated by representations that encode both a viewer's recent and normative exposure to faces. The finding that age perception is subject to strong top-down influences based on our immediate experience has implications for our understanding of perceptual processes involved in face perception, and for improving accuracy of age estimation in important real-world tasks.

Attenuation of visual evoked responses to hand and saccade-initiated flashes.

Sensory attenuation refers to reduced brain responses to self-initiated sensations relative to those produced by the external world. It is a low-level process that may be linked to higher-level cognitive tasks such as reality monitoring. The phenomenon is often explained by prediction error mechanisms of universal applicability to sensory modality; however, it is most widely reported for auditory stimuli resulting from self-initiated hand movements. The present series of event-related potential (ERP) experiments explored the generalizability of sensory attenuation to the visual domain by exposing participants to flashes initiated by either their own button press or volitional saccade and comparing these conditions to identical, computer-initiated stimuli. The key results showed that the largest reduction of anterior visual N1 amplitude occurred for saccade-initiated flashes, while button press-initiated flashes evoked an intermediary response between the saccade-initiated and externally initiated conditions. This indicates that sensory attenuation occurs for visual stimuli and suggests that the degree of electrophysiological attenuation may relate to the causal likelihood of pairings between the type of motor action and the modality of its sensory response.

Attenuation of auditory evoked potentials for hand and eye-initiated sounds.

Reduction of auditory event-related potentials (ERPs) to self-initiated sounds has been considered evidence for a predictive model in which copies of motor commands suppress sensory representations of incoming stimuli. However, in studies which involve arbitrary auditory stimuli evoked by sensory-unspecific motor actions, learned associations may underlie ERP differences. Here, in a new paradigm, eye motor output generated auditory sensory input, a naïve action-sensation contingency. We measured the electroencephalogram (EEG) of 40 participants exposed to pure tones, which they produced with either a button-press or volitional saccade. We found that button-press-initiated stimuli evoked reduced amplitude compared to externally initiated stimuli for both the N1 and P2 ERP components, whereas saccade-initiated stimuli evoked intermediate attenuation at N1 and no reduction at P2. These results indicate that the motor-to-sensory mapping involved in speech production may be partly generalized to other contingencies, and that learned associations also contribute to the N1 attenuation effect.

Who are you expecting? Biases in face perception reveal prior expectations for sex and age.

A person's appearance contains a wealth of information, including indicators of their sex and age. Because first impressions can set the tone of subsequent relationships, it is crucial we form an accurate initial impression. Yet prior expectation can bias our decisions: Studies have reported biases to respond "male" when asked to report a person's sex from an image of their face and to place their age closer to their own. Perceptual expectation effects and cognitive response biases may both contribute to these inaccuracies. The current research used a Bayesian modeling approach to establish the perceptual biases involved when estimating the sex and age of an individual from their face. We demonstrate a perceptual bias for male and older faces evident under conditions of uncertainty. This suggests the well-established male bias is perceptual in origin and may be impervious to cognitive control. In comparison, the own age anchor effect is not operationalized at the perceptual level: The perceptual expectation is for a face of advanced age. Thus, distinct biases in the estimation of age operate at the perceptual and cognitive levels.

Spatial compression: Dissociable effects at the time of saccades and blinks.

Various studies have identified systematic errors, such as spatial compression, when observers report the locations of objects displayed around the time of saccades. Localization errors also occur when holding spatial representations in visual working memory. Such errors, however, have not been examined in the context of eye blinks. In this study, we examined the effects of blinks and saccades when observers reproduced the locations of a set of briefly presented, randomly placed discs. Performance was compared with a fixation-only condition in which observers simply held these representations in working memory for the same duration; this allowed us to elucidate the relationship between the perceptual phenomena related to blinks, saccades, and visual working memory. Our results indicate that the same amount of spatial compression is experienced prior to a blink as is experienced in the control fixation-only condition, suggesting that blinks do not increase compression above that occurring from holding a spatial representation in visual memory. Saccades, however, tend to increase these compression effects and produce translational shifts both toward and away from saccade targets (depending on the time of the saccade onset in relation to the stimulus offset). A higher numerosity recall capacity was also observed when stimuli were presented prior to a blink in comparison with the other conditions. These findings reflect key differences underlying blinks and saccades in terms of spatial compression and translational shifts. Such results suggest that separate mechanisms maintain perceptual stability across these visual events.

Attentional bias modification facilitates attentional control mechanisms: evidence from eye tracking.

Social anxiety is thought to be maintained by biased attentional processing towards threatening information. Research has further shown that the experimental attenuation of this bias, through the implementation of attentional bias modification (ABM), may serve to reduce social anxiety vulnerability. However, the mechanisms underlying ABM remain unclear. The present study examined whether inhibitory attentional control was associated with ABM. A non-clinical sample of participants was randomly assigned to receive either ABM or a placebo task. To assess pre-post changes in attentional control, participants were additionally administered an emotional antisaccade task. ABM participants exhibited a subsequent shift in attentional bias away from threat as expected. ABM participants further showed a subsequent decrease in antisaccade cost, indicating a general facilitation of inhibitory attentional control. Mediational analysis revealed that the shift in attentional bias following ABM was independent to the change in attentional control. The findings suggest that the mechanisms of ABM are multifaceted.

Infant perceptual development for faces and spoken words: an integrated approach.

There are obvious differences between recognizing faces and recognizing spoken words or phonemes that might suggest development of each capability requires different skills. Recognizing faces and perceiving spoken language, however, are in key senses extremely similar endeavors. Both perceptual processes are based on richly variable, yet highly structured input from which the perceiver needs to extract categorically meaningful information. This similarity could be reflected in the perceptual narrowing that occurs within the first year of life in both domains. We take the position that the perceptual and neurocognitive processes by which face and speech recognition develop are based on a set of common principles. One common principle is the importance of systematic variability in the input as a source of information rather than noise. Experience of this variability leads to perceptual tuning to the critical properties that define individual faces or spoken words versus their membership in larger groupings of people and their language communities. We argue that parallels can be drawn directly between the principles responsible for the development of face and spoken language perception.

Determinants of motion response anisotropies in human early visual cortex: the role of configuration and eccentricity.

Anisotropies in the cortical representation of various stimulus parameters can reveal the fundamental mechanisms by which sensory properties are analysed and coded by the brain. One example is the preference for motion radial to the point of fixation (i.e. centripetal or centrifugal) exhibited in mammalian visual cortex. In two experiments, this study used functional magnetic resonance imaging (fMRI) to explore the determinants of these radial biases for motion in functionally-defined areas of human early visual cortex, and in particular their dependence upon eccentricity which has been indicated in recent reports. In one experiment, the cortical response to wide-field random dot kinematograms forming 16 different complex motion patterns (including centrifugal, centripetal, rotational and spiral motion) was measured. The response was analysed according to preferred eccentricity within four different eccentricity ranges. Response anisotropies were characterised by enhanced activity for centripetal or centrifugal patterns that changed systematically with eccentricity in visual areas V1-V3 and hV4 (but not V3A/B or V5/MT+). Responses evolved from a preference for centrifugal over centripetal patterns close to the fovea, to a preference for centripetal over centrifugal at the most peripheral region stimulated, in agreement with previous work. These effects were strongest in V2 and V3. In a second experiment, the stimuli were restricted to within narrow annuli either close to the fovea (0.75-1.88°) or further in the periphery (4.82-6.28°), in a way that preserved the local motion information available in the first experiment. In this configuration a preference for radial motion (centripetal or centrifugal) persisted but the dependence upon eccentricity disappeared. Again this was clearest in V2 and V3. A novel interpretation of the dependence upon eccentricity of motion anisotropies in early visual cortex is offered that takes into account the spatiotemporal "predictability" of the moving pattern. Such stimulus predictability, and its relationship to models of predictive coding, has found considerable support in recent years in accounting for a number of other perceptual and neural phenomena.

Biased saccadic responses to emotional stimuli in anxiety: an antisaccade study.

Research suggests that anxiety is maintained by an attentional bias to threat, and a growing base of evidence suggests that anxiety may additionally be associated with the deficient attentional processing of positive stimuli. The present study sought to examine whether such anxiety-linked attentional biases were associated with either stimulus driven or attentional control mechanisms of attentional selectivity. High and low trait anxious participants completed an emotional variant of an antisaccade task, in which they were required to prosaccade towards, or antisaccade away from a positive, neutral or threat stimulus, while eye movements were recorded. While low anxious participants were found to be slower to saccade in response to positive stimuli, irrespectively of whether a pro- or antisaccade was required, such a bias was absent in high anxious individuals. Analysis of erroneous antisaccades further revealed at trend level, that anxiety was associated with reduced peak velocity in response to threat. The findings suggest that anxiety is associated with the aberrant processing of positive stimuli, and greater compensatory efforts in the inhibition of threat. The findings further highlight the relevance of considering saccade peak velocity in the assessment of anxiety-linked attentional processing.