Upper-lower visual field asymmetries in oculomotor inhibition of emotional distractors

Exploring the Social Environment with the Eyes: A Review of the Impact of Facial Stimuli on Saccadic Trajectories

Eye movement parameters can be highly informative regarding how people explore the social environment around them. This theoretical review examines how human faces and their features (e.g., eye-gaze direction, emotional expressions) can modulate saccadic trajectories. In the first part, studies in which facial stimuli were presented in a central location, such as during a face-to-face social interaction, are illustrated. The second part focuses on studies in which facial stimuli were placed in the periphery. Together, these works confirm the presence of an intriguing link between eye movements and facial processing, and invite consideration of saccadic trajectories as a useful (and still underused) opportunity to track ongoing mechanisms that support the social vision. Some directions for future research are also discussed.

Atypical visual field asymmetries in redundancy masking

Redundancy masking is the reduction of the perceived number of items in repeating patterns. It shares a number of characteristics with crowding, the impairment of target identification in visual clutter. Crowding strongly depends on the location of the target in the visual field. For example, it is stronger in the upper compared to the lower visual field and is usually weakest on the horizontal meridian. This pattern of visual field asymmetries is common in spatial vision, as revealed by tasks measuring, for example, spatial resolution and contrast sensitivity. Here, to characterize redundancy masking and reveal its similarities to and differences from other spatial tasks, we investigated whether redundancy masking shows the same typical visual field asymmetries. Observers were presented with three to six radially arranged lines at 10° eccentricity at one of eight locations around fixation and were asked to report the number of lines. We found asymmetries that differed pronouncedly from those found in crowding. Redundancy masking did not differ between upper and lower visual fields. Importantly, redundancy masking was stronger on the horizontal meridian than on the vertical meridian, the opposite of what is usually found in crowding. These results show that redundancy masking diverges from crowding in regard to visual field asymmetries, suggesting different underlying mechanisms of redundancy masking and crowding. We suggest that the observed atypical visual field asymmetries in redundancy masking are due to the superior extraction of regularity and a more pronounced compression of visual space on the horizontal compared to the vertical meridian.

Asymmetries in visual acuity around the visual field

Human vision is heterogeneous around the visual field. At a fixed eccentricity, performance is better along the horizontal than the vertical meridian and along the lower than the upper vertical meridian. These asymmetric patterns, termed performance fields, have been found in numerous visual tasks, including those mediated by contrast sensitivity and spatial resolution. However, it is unknown whether spatial resolution asymmetries are confined to the cardinal meridians or whether and how far they extend into the upper and lower hemifields. Here, we measured visual acuity at isoeccentric peripheral locations (10 deg eccentricity), every 15° of polar angle. On each trial, observers judged the orientation (± 45°) of one of four equidistant, suprathreshold grating stimuli varying in spatial frequency (SF). On each block, we measured performance as a function of stimulus SF at 4 of 24 isoeccentric locations. We estimated the 75%-correct SF threshold, SF cutoff point (i.e., chance-level), and slope of the psychometric function for each location. We found higher SF estimates (i.e., better acuity) for the horizontal than the vertical meridian and for the lower than the upper vertical meridian. These asymmetries were most pronounced at the cardinal meridians and decreased gradually as the angular distance from the vertical meridian increased. This gradual change in acuity with polar angle reflected a shift of the psychometric function without changes in slope. The same pattern was found under binocular and monocular viewing conditions. These findings advance our understanding of visual processing around the visual field and help constrain models of visual perception.

Retinotopy of emotion: Perception of negatively valenced stimuli presented at different spatial locations as revealed by event-related potentials

Scarce previous data on how the location where an emotional stimulus appears in the visual scene modulates its perception suggest that, for functional reasons, a perceptual advantage may exist, vertically, for stimuli presented at the lower visual field (LoVF) and, horizontally, for stimuli presented at the left visual field (LeVF). However, this issue has been explored through a limited number of spatial locations, usually in a single spatial dimension (e.g., horizontal) and invariant eccentricities. Event-related potentials (ERPs) were recorded from 39 participants perceiving brief neutral (wheels) and emotional stimuli (spiders) presented at 17 different locations, one foveal and 16 at different peripheral coordinates. As a secondary scope, we explored the role of the magnocellular (M) and the parvocellular (P) visual pathways by presenting an isoluminant/heterochromatic (P-biased) and a heteroluminant/isochromatic version (M-biased) of each stimulus. Emo > Neu effects were observed in PN1 (120 ms) for stimuli located at fovea, and in PN2 (215 ms) for stimuli located both at fovea and diverse peripheral regions. A factorial approach to these effects further revealed that: (a) emotional stimuli presented in the periphery are efficiently perceived, without evident decrease from para- to perifovea; (b) peripheral Emo > Neu effects are reflected 95 ms later than foveal Emo > Neu effects in ERPs; (c) LoVF is more involved than UVF in these effects; (d) our data fail to support the LeVF advantage previously reported, and (e) Emo > Neu effects were significant for both M and P stimuli.

Trypophobic images induce oculomotor capture and inhibition

It is known that unpleasant images capture our attention. However, the causes of the emotions evoked by these images can vary. Trypophobia is the fear of clustered objects. A recent study claimed that this phobia is elicited by the specific power spectrum of such images. In the present study, we measured saccade trajectories to examine how trypophobic images possessing a characteristic power spectrum affect visual attention. The participants' task was to make a saccade in the direction that was indicated by a cue. Four irrelevant images with different emotional content were presented as periphery distractors at 0 ms, 150 ms, and 450 ms in terms of cue-image onset asynchrony. The irrelevant images consisted of trypophobic, fearful, or neutral scenes. The presence of saccade trajectory deviations induced by trypophobic images suggest that intact trypophobic images oriented attention to their location. Moreover, when the images were phase scrambled, the saccade curved away from the trypophobic images, suggesting that trypophobic power spectra also triggered attentional capture, which was weak and then led to inhibition. These findings suggest that not only the power spectral characteristics but also the gist of a trypophobic image affect attentional deployment.

Counter-regulation in affective attentional biases: Evidence in the additional singleton paradigm

We investigated motivational influences on affective processing biases; specifically, we were interested in whether anticipating positive versus negative future outcomes during goal pursuit affects attentional biases toward positive or negative stimuli. Attentional valence biases were assessed with the additional singleton task, with the task-irrelevant singleton colors being positive, negative or neutral. The motivational relevance of colors was established in a preceding task: In a balanced design, one color acquired positive valence by indicating the chance to win money, and a different color acquired negative valence by indicating the danger to lose money. Blocks of the additional singleton task were associated with either the chance of winning money (positive outcome focus) or the danger of losing money (negative outcome focus). We found an interaction of outcome focus and singleton valence in the accuracy rates, indicating an incongruency effect: Attentional capture was stronger for positive (negative) singletons in the negative (positive) outcome focus conditions. This result further corroborates the counter-regulation hypothesis, extending previous findings on the motivational top-down regulation of affective processing to the domain of early attentional processes.

Recognition memory for low- and high-frequency-filtered emotional faces: Low spatial frequencies drive emotional memory enhancement, whereas high spatial frequencies drive the emotion-induced recognition bias

This article deals with two well-documented phenomena regarding emotional stimuli: emotional memory enhancement-that is, better long-term memory for emotional than for neutral stimuli-and the emotion-induced recognition bias-that is, a more liberal response criterion for emotional than for neutral stimuli. Studies on visual emotion perception and attention suggest that emotion-related processes can be modulated by means of spatial-frequency filtering of the presented emotional stimuli. Specifically, low spatial frequencies are assumed to play a primary role for the influence of emotion on attention and judgment. Given this theoretical background, we investigated whether spatial-frequency filtering also impacts (1) the memory advantage for emotional faces and (2) the emotion-induced recognition bias, in a series of old/new recognition experiments. Participants completed incidental-learning tasks with high- (HSF) and low- (LSF) spatial-frequency-filtered emotional and neutral faces. The results of the surprise recognition tests showed a clear memory advantage for emotional stimuli. Most importantly, the emotional memory enhancement was significantly larger for face images containing only low-frequency information (LSF faces) than for HSF faces across all experiments, suggesting that LSF information plays a critical role in this effect, whereas the emotion-induced recognition bias was found only for HSF stimuli. We discuss our findings in terms of both the traditional account of different processing pathways for HSF and LSF information and a stimulus features account. The double dissociation in the results favors the latter account-that is, an explanation in terms of differences in the characteristics of HSF and LSF stimuli.

Attentional enhancement for positive and negative tones at an early stage of auditory processing

We report an event-related potential (ERP) study based on the hypothesis that valenced (i.e., positive and/or negative) tones are prioritized over neutral ones at an early, perceptual stage of auditory processing. In order to avoid perceptual confounds, we induced valence experimentally during a learning phase by assigning positive, negative, and neutral valences to tone-frequencies in a balanced design. In a subsequent test phase, EEG was recorded while these tones were entirely task-irrelevant. The amplitude of the auditory N1 was increased for valenced compared with neutral tones, indicating enhanced attention. While behavioral results of the learning phase, and both implicit and explicit measures of tone evaluation indicated differentiation between positive and negative valence, there was no such differentiation on the N1 amplitude. Our results suggest that it is the general relevance of the valenced tones that governs early attentional processes.

Common Priority Map for Selection History, Reward and Emotion in the Oculomotor System

In natural scenes, many objects compete for visual selection. However, it is not always clear why certain objects win this competition. I will demonstrate that the eye movement system lives in a constant state of competition among different oculomotor programs. This competition is not limited to the competition between the current goals of the observer and salient objects in the environment but incorporates independent influences from memory, reward, and emotional systems. These involuntary and automatic biases often overcome the goal-directed selection and expose severe limits in goal-driven control. There is also a striking similarity in the way that these very different sources of bias activate the oculomotor system and compete for representation. The inputs from various information sources are integrated in the common map in the oculomotor system for the sole purpose of improving the efficiency of oculomotor selection.

Attentional capture by evaluative stimuli: gain- and loss-connoting colors boost the additional-singleton effect

In a valence induction task, one color acquired positive valence by indicating the chance to win money (in the case of fast and correct responses), and a different color acquired negative valence by indicating the danger to lose money (in the case of slow or incorrect responses). In the additional-singleton trials of a visual search task, the task-irrelevant singleton color was either the positive one, the negative one, or one of two neutral colors. We found an additional-singleton effect (i.e., longer RTs with a singleton color than in the no-singleton control condition). This effect was significantly increased for the two valent colors (with no differences between them) relative to the two neutral colors (with no differences between them, either). This result favors the hypothesis that the general relevance of stimuli elicits attentional capture, rather than the negativity bias hypothesis.

Distractor evoked deviations of saccade trajectory are modulated by fixation activity in the superior colliculus: computational and behavioral evidence

Previous studies have shown that saccades may deviate towards or away from task irrelevant visual distractors. This observation has been attributed to active suppression (inhibition) of the distractor location unfolding over time: early in time inhibition at the distractor location is incomplete causing deviation towards the distractor, while later in time when inhibition is complete the eyes deviate away from the distractor. In a recent computational study, Wang, Kruijne and Theeuwes proposed an alternative theory that the lateral interactions in the superior colliculus (SC), which are characterized by short-distance excitation and long-distance inhibition, are sufficient for generating both deviations towards and away from distractors. In the present study, we performed a meta-analysis of the literature, ran model simulations and conducted two behavioral experiments to further explore this unconventional theory. Confirming predictions generated by the model simulations, the behavioral experiments show that a) saccades deviate towards close distractors and away from remote distractors, and b) the amount of deviation depends on the strength of fixation activity in the SC, which can be manipulated by turning off the fixation stimulus before or after target onset (Experiment 1), or by varying the eccentricity of the target and distractor (Experiment 2).

Cultural influences on oculomotor inhibition of remote distractors: evidence from saccade trajectories

This study investigated whether low-level attentional processes as indicated by saccade trajectories are modulated by higher-order factors as indicated by participants' cultural background. We hypothesized that if the East Asian participants engage in context-dependent attentional processing to a greater extent than the Western participants, then the magnitude of the distractor effect on saccade trajectories (Doyle & Walker, 2001) should be larger with the East Asian participants than with the Western participants. Participants executed vertical saccades towards targets presented on the vertical meridian above or below fixation. Simultaneously with the target, a distractor appeared in one of the screen quadrants. Consistently with our hypothesis, we found evidence that the saccades of the Chinese participants tended to curve away from the distractors more strongly than the saccades of the German participants. However, this effect was restricted to the upper distractors and the lower targets. The findings are discussed in terms of cross-cultural differences in distractor-related activation and inhibition and functional specialization of hemifields.