High Spatial Frequency Stimuli Research Articles

High Spatial Frequency Stimuli Amplify Visual Integration Deficits in Schizophrenia and Bipolar Disorder

High Spatial Frequency Stimuli Amplify Visual Integration Deficits in Schizophrenia and Bipolar Disorder

Visual experience has opposing influences on the quality of stimulus representation in adult primary visual cortex.

Transient dark exposure, typically 7-10 days in duration, followed by light reintroduction is an emerging treatment for improving the restoration of vision in amblyopic subjects whose occlusion is removed in adulthood. Dark exposure initiates homeostatic mechanisms that together with light-induced changes in cellular signaling pathways result in the re-engagement of juvenile-like plasticity in the adult such that previously deprived inputs can gain cortical territory. It is possible that dark exposure itself degrades visual responses, and this could place constraints on the optimal duration of dark exposure treatment. To determine whether eight days of dark exposure has a lasting negative impact on responses to classic grating stimuli, neural activity was recorded before and after dark exposure in awake head-fixed mice using two-photon calcium imaging. Neural discriminability, assessed using classifiers, was transiently reduced following dark exposure; a decrease in response reliability across a broad range of spatial frequencies likely contributed to the disruption. Both discriminability and reliability recovered. Fixed classifiers were used to demonstrate that stimulus representation rebounded to the original, pre-deprivation state, thus dark exposure did not appear to have a lasting negative impact on visual processing. Unexpectedly, we found that dark exposure significantly stabilized orientation preference and signal correlation. Our results reveal that natural vision exerts a disrupting influence on the stability of stimulus preference for classic grating stimuli and, at the same time, improves neural discriminability for both low and high-spatial frequency stimuli.

Spatial suppression of chromatic motion

Center-surround antagonism, as a ubiquitous feature in visual processing, usually leads to inferior perception for a large stimulus compared to a small one. For example, it is more difficult to judge the motion direction of a large high-contrast pattern than that of a small one. However, this spatial suppression in the motion dimension was only reported for luminance motion, and was not found for chromatic motion. Given that center-surround suppression only occurs for strong visual inputs, we hypothesized that previous failure in finding spatial suppression of chromatic motion might be due to weak chromatic motion being induced with stimuli of limited parameters. In this study, we used phase-shift discrimination and motion-direction discrimination tasks to measure motion spatial suppression induced by stimuli of two spatial frequencies (0.5 and 2 cpd) and two contrasts (low and high). We found that spatial suppression of the chromatic motion was stably observed for stimuli of high spatial frequency (2 cpd) and high contrast and spatial summation occurred for stimuli of low spatial frequency (0.5 cpd). Intriguingly, there was no correlations between the motion spatial suppressions of luminance motion and chromatic motion, implying that the two types of spatial suppression are not originated from the same neural processing. Our findings indicate that spatial suppression also exists for chromatic motion, and the mechanisms underlying the spatial suppression of chromatic motion is different from that of luminance motion.

Selective postsaccadic enhancement of motion perception

Saccadic eye movements can drastically affect motion perception: during saccades, the stationary surround is swept rapidly across the retina and contrast sensitivity is suppressed. However, after saccades, contrast sensitivity is enhanced for color and high-spatial frequency stimuli and reflexive tracking movements known as ocular following responses (OFR) are enhanced in response to large field motion. Additionally, OFR and postsaccadic enhancement of neural activity in primate motion processing areas are well correlated. It is not yet known how this postsaccadic enhancement arises. Therefore, we tested if the enhancement can be explained by changes in the balance of centre-surround antagonism in motion processing, where spatial summation is favoured at low contrasts and surround suppression is favoured at high contrasts. We found motion perception was selectively enhanced immediately after saccades for high spatial frequency stimuli, consistent with previously reported selective postsaccadic enhancement of contrast sensitivity for flashed high spatial frequency stimuli. The observed enhancement was also associated with changes in spatial summation and suppression, as well as contrast facilitation and inhibition, suggesting that motion processing is augmented to maximise visual perception immediately after saccades. The results highlight that spatial and contrast properties of underlying neural mechanisms for motion processing can be affected by an antecedent saccade for highly detailed stimuli and are in line with studies that show behavioural and neuronal enhancement of motion processing in non-human primates.

FMRI representational similarity analysis reveals graded preferences for chromatic and achromatic stimulus contrast across human visual cortex

Human visual cortex is partitioned into different functional areas that, from lower to higher, become increasingly selective and responsive to complex feature dimensions. Here we use a Representational Similarity Analysis (RSA) of fMRI-BOLD signals to make quantitative comparisons across LGN and multiple visual areas of the low-level stimulus information encoded in the patterns of voxel responses. Our stimulus set was picked to target the four functionally distinct subcortical channels that input visual cortex from the LGN: two achromatic sinewave stimuli that favor the responses of the high-temporal magnocellular and high-spatial parvocellular pathways, respectively, and two chromatic stimuli isolating the L/M-cone opponent and S-cone opponent pathways, respectively. Each stimulus type had three spatial extents to sample both foveal and para-central visual field. With the RSA, we compare quantitatively the response specializations for individual stimuli and combinations of stimuli in each area and how these change across visual cortex. First, our results replicate the known response preferences for motion/flicker in the dorsal visual areas. In addition, we identify two distinct gradients along the ventral visual stream. In the early visual areas (V1–V3), the strongest differential representation is for the achromatic high spatial frequency stimuli, suitable for form vision, and a very weak differentiation of chromatic versus achromatic contrast. Emerging in ventral occipital areas (V4, VO1 and VO2), however, is an increasingly strong separation of the responses to chromatic versus achromatic contrast and a decline in the high spatial frequency representation. These gradients provide new insight into how visual information is transformed across the visual cortex.

Interaction between motion scales: When performance in motion discrimination is worse for a compound stimulus than for its integrating components

Motion direction discrimination becomes impaired when combinations of drifting high spatial frequency (HSF) and static low spatial frequency (LSF) patterns are merged into a compound stimulus. Such impairment has been suggested to occur due to an interaction between motion sensors tuned to coarse and fine scale spatial patterns. This interaction is modulated by different stimulus parameters like temporal frequency, size, the spectral components mixed, and their relative contrast. The present research precisely aims to explore in a deeper way the interaction’s dependency upon the spatial frequency and the relative contrast of the components when both move coherently. Two experiments were therefore performed measuring duration thresholds (Experiment 1) and proportion of correct responses (Experiment 2) in a motion direction discrimination task. Stimuli were vertical Gabor patches of 4 deg diameter horizontally drifting with a speed of 2 deg/sec. Simple LSF and HSF stimuli as well as complex stimuli where both components moved coherently (LSFm + HSFm) were used. These were grouped in the following LSF and HSF pairs: 0.25–0.75, 0.5–1.5, 1–3 and 2–6 c/deg. Each component had a Michelson contrast of 28% or 7%, giving rise to different relative contrast combinations. Most interestingly, the results show a decrease in performance for complex stimuli with respect to each of their simple components when the LSF component has a lower contrast than the HSF one. The decrease depends on the particular spatial frequencies mixed in a stimulus. Further knowledge about the inhibitory mechanism is thus provided, revealing its joint dependency upon contrast and spatial frequency.

Emotion Recognition in Low-Spatial Frequencies Is Partly Preserved following Traumatic Brain Injury.

After a Traumatic Brain Injury (TBI), emotion recognition is typically impaired. This is commonly attributed to widespread multifocal damage in cortical areas involved in emotion processing as well as to Diffuse Axonal Injury (DAI). However, current models suggest that emotional recognition is subserved by a distributed network cantered on the amygdala, which involves both cortical and subcortical structures. While the cortical system is preferentially tuned to process high spatial frequencies, the subcortical networks are more sensitive to low-spatial frequencies. The aim of this study was to evaluate whether emotion perception from low-spatial frequencies underpinning the subcortical system is relatively preserved in TBI patients. We tested a group of 14 subjects with severe TBI and 20 matched healthy controls. Each participant was asked to recognize the emotion expressed by each stimulus that consisted of happy and fearful faces, filtered for their low and high spatial frequencies components. Results in TBI patients' performances showed that low-spatial frequency expressions were recognized with higher accuracy and faster reaction times when compared to high spatial frequency stimuli. On the contrary, healthy controls did not show any effect in the two conditions, neither for response accuracy nor for reaction times. The outcomes of this study indicate that emotion perception from low-spatial frequencies is relatively preserved in TBI, thereby suggesting spare of functioning in the subcortical system in mediating emotion recognition.

Neuronal basis of perceptual learning in striate cortex.

It is well known that, in humans, contrast sensitivity training at high spatial frequency (SF) not only leads to contrast sensitivity improvement, but also results in an improvement in visual acuity as assessed with gratings (direct effect) or letters (transfer effect). However, the underlying neural mechanisms of this high spatial frequency training improvement remain to be elucidated. In the present study, we examined four properties of neurons in primary visual cortex (area 17) of adult cats that exhibited significantly improved acuity after contrast sensitivity training with a high spatial frequency grating and those of untrained control cats. We found no difference in neuronal contrast sensitivity or tuning width (Width) between the trained and untrained cats. However, the trained cats showed a displacement of the cells’ optimal spatial frequency (OSF) to higher spatial frequencies as well as a larger neuronal signal-to-noise ratio (SNR). Furthermore, both the neuronal differences in OSF and SNR were significantly correlated with the improvement of acuity measured behaviorally. These results suggest that striate neurons might mediate the perceptual learning-induced improvement for high spatial frequency stimuli by an alteration in their spatial frequency representation and by an increased SNR.

Spatial Frequency Modulates the Degree of Illusory Second Flash Perception.

When a brief single flash is presented simultaneously with two brief beeps, the number of presented flashes is often perceived as two. This phenomenon is referred to as the fission illusion. Several effects related to the fission illusion have been investigated using both psychophysical and neurophysiological methods. The present study examined the effects of spatial frequency on the fission illusion. At a low spatial frequency, transient channels respond preferably; conversely, sustained channels respond preferably at a high spatial frequency. Sustained channels differ in temporal properties from transient channels and are characterized by poor temporal resolution and slow-onset responses. In our previous study, visual stimuli presented at a slow processing speed were not conducive to the fission illusion. Therefore, we hypothesized that the fission illusion would not be difficult to observe when using high spatial frequencies. The results indicated that the degree of the perceived illusory second flash was reduced when spatial frequency was high as compared to when it was is low. Furthermore, according to signal detection theory, this difference between high and low spatial frequencies was not attributed to participants' response biases. Therefore, the fission illusion likely will not occur in conditions of slow processing speed and long response latencies in sustained channels, which respond preferably to high spatial frequency stimuli. Overall, the results indicated that the fission illusion was affected by temporal characteristics of lower-order sensory processing stages.

On the use of cues to assess attention in dyslexia.

On the use of cues to assess attention in dyslexia.

Impact of primary spherical aberration, spatial frequency and Stiles Crawford apodization on wavefront determined refractive error: a computational study

We tested the hypothesis that pupil apodization is the basis for central pupil bias of spherical refractions in eyes with spherical aberration. We employed Fourier computational optics in which we vary spherical aberration levels, pupil size, and pupil apodization (Stiles Crawford Effect) within the pupil function, from which point spread functions and optical transfer functions were computed. Through-focus analysis determined the refractive correction that optimized retinal image quality. For a large pupil (7 mm), as spherical aberration levels increase, refractions that optimize the visual Strehl ratio mirror refractions that maximize high spatial frequency modulation in the image and both focus a near paraxial region of the pupil. These refractions are not affected by Stiles Crawford Effect apodization. Refractions that optimize low spatial frequency modulation come close to minimizing wavefront RMS, and vary with level of spherical aberration and Stiles Crawford Effect. In the presence of significant levels of spherical aberration (e.g. C(4)(0) = 0.4 μm, 7 mm pupil), low spatial frequency refractions can induce -0.7 D myopic shift compared to high SF refraction, and refractions that maximize image contrast of a three cycle per degree square-wave grating can cause -0.75 D myopic drift relative to refractions that maximize image sharpness. Because of small depth of focus associated with high spatial frequency stimuli, the large change in dioptric power across the pupil caused by spherical aberration limits the effective aperture contributing to the image of high spatial frequencies. Thus, when imaging high spatial frequencies, spherical aberration effectively induces an annular aperture defining that portion of the pupil contributing to a well-focused image. As spherical focus is manipulated during the refraction procedure, the dimensions of the annular aperture change. Image quality is maximized when the inner radius of the induced annulus falls to zero, thus defining a circular near paraxial region of the pupil that determines refraction outcome.

Repetition Blindness for Natural Images of Objects with Viewpoint Changes

When stimuli are repeated in a rapid serial visual presentation (RSVP), observers sometimes fail to report the second occurrence of a target. This phenomenon is referred to as “repetition blindness” (RB). We report an RSVP experiment with photographs in which we manipulated object viewpoints between the first and second occurrences of a target (0°, 45°, or 90° changes), and spatial frequency (SF) content. Natural images were spatially filtered to produce low, medium, or high SF stimuli. RB was observed for all filtering conditions. Surprisingly, for full-spectrum (FS) images, RB increased significantly as the viewpoint reached 90°. For filtered images, a similar pattern of results was found for all conditions except for medium SF stimuli. These findings suggest that object recognition in RSVP are subtended by viewpoint-specific representations for all spatial frequencies except medium ones.

Spatiotemporal receptive field structures in retinogeniculate connections of cat

The spatial structure of the receptive field (RF) of cat lateral geniculate nucleus (LGN) neurons is significantly elliptical, which may provide a basis for the orientation tuning of LGN neurons, especially at high spatial frequency stimuli. However, the input mechanisms generating this elliptical RF structure are poorly defined. We therefore compared the spatiotemporal RF structures of pairs of retinal ganglion cells (RGCs) and LGN neurons that form monosynaptic connections based on the cross-correlation analysis of their firing activities. We found that the spatial RF structure of both RGCs and LGN neurons were comparably elliptical and oriented in a direction toward the area centralis. Additionally, the spatial RF structures of pairs with the same response sign were often overlapped and similarly oriented. We also found there was a small population of pairs with RF structures that had the opposite response sign and were spatially displaced and independently oriented. Finally, the temporal RF structure of an RGC was tightly correlated with that of its target LGN neuron, though the response duration of the LGN neuron was significantly longer. Our results suggest that the elliptical RF structure of an LGN neuron is mainly inherited from the primary projecting RGC and is affected by convergent inputs from multiple RGCs. We discuss how the convergent inputs may enhance the stimulus feature sensitivity of LGN neurons.

Relationship between orientation sensitivity and spatiotemporal receptive field structures of neurons in the cat lateral geniculate nucleus

Although it is thought that orientation selectivity first emerges in the primary visual cortex, several studies have reported that neurons in the cat lateral geniculate nucleus (LGN) are sensitive to stimulus orientation, especially for high spatial frequency (SF) stimuli. To understand how this orientation sensitivity emerges, we investigated the spatiotemporal structures of linear receptive fields (RFs) of LGN neurons. Orientation tunings at several SFs were measured using sinusoidal drifting grating stimuli. Fine spatiotemporal structures of the linear RFs were measured using a reverse correlation technique and two-dimensional dynamic Gaussian white noise stimuli. A non-linear response modulation function was estimated by comparing measured responses with responses predicted from a linear RF structure. Although we found that a population of LGN neurons exhibited significantly elongated linear RF centers and that the angles of the long axes corresponded well to the preferred orientations, the orientation tunings predicted from the linear RFs were significantly broader than those measured. These results suggest that orientation-tuned non-linear response modulation induced by stimulation outside the classical RF contributes to the sharp orientation tuning seen in LGN neurons.

Distinct role of spatial frequency in dissociative reading of ideograms and phonograms: An fMRI study

It has been proposed that distinct neural circuits are activated by reading Japanese ideograms (Kanji) and phonograms (Kana). By measuring high-density event-related potentials, we recently reported that spatial frequency (SF) information is responsible for the dissociation between Kanji and Kana reading. In particular, we found close links between Kana and low SF (LSF) information and between Kanji and high SF (HSF) information. However, it remains unclear which brain regions contribute to this dissociation. To determine this, we performed functional magnetic resonance imaging while presenting unfiltered or spatially filtered Kanji and Kana word stimuli to healthy native Japanese subjects. Fourier analysis revealed that Kanji and Kana stimuli were characterized by HSF and LSF information, respectively. When presented with either type of unfiltered stimulus (Kanji or Kana), the bilateral inferior temporal (IT, BA 37) regions were activated compared to the resting condition. Kana but not Kanji reading also activated the bilateral inferior parietal lobules (IPL, BA 40). When we compared Kanji and Kana reading directly, the left IT region was significantly activated by Kanji reading, while significant activation of the left IPL was observed during Kana reading. In response to filtered HSF stimuli, the Kanji reading minus Kana reading comparison revealed significant activation of the left IT region but not the left IPL. Conversely, significant activation of the left IPL but not the left IT region occurred in the Kana reading minus Kanji reading comparison for filtered LSF stimuli. These results suggest that Kanji and Kana engage a relatively overlapping network, within which the left IT is more involved in Kanji processing, while the left IPL contributes more to Kana processing. The preferential engagements of these brain regions could reflect the close links between Kana and LSF information, and between Kanji and HSF information. Therefore, this study provides further evidence that SF contributes to the dissociation between Kanji and Kana reading.

Active Vision: Fixational Eye Movements Help Seeing Space in Time

The significance of the miniature eye movements that we make during visual fixation has been intensely debated for the last 80 years. Recent studies have revealed that these motions of the eyes fulfill an important functional role: helping to extract useful information from natural scenes.

Atypical neural response to high and low spatial frequency stimuli in a rare case of visual perseveration

Event Abstract Back to Event Atypical neural response to high and low spatial frequency stimuli in a rare case of visual perseveration Mark A. Williams1*, Bhuvanesh Awasthi1, 2, Paul F. Sowman1, 2, Matthew S. Finkbeiner1, 2 and Anina N. Rich1, 2 1 Macquarie University, Cognitive Science, Australia 2 Macquarie University, Centre for Cognition and its Disorders, Australia Visual perseveration is an unusual pathology that results in visual persistence of images in the absence of the original stimulus. There is often a short delay between the visual stimulation and the corresponding mental image or internal representation. The mental image usually disappears within seconds, although it may persist for several minutes and in some cases for much longer. Here we present a case of a young male, M, presenting with severe long-term visual perseveration of unknown eitiology who performs normally on all previous clinical examinations. His images often persist for several minutes and cause major disruption to his life. The onset occurred in his late teens but there is no known trauma. Structural MRI scanning revealed no obvious neurological damage. We performed Magnetoencephalograhy (MEG) while presenting spatially filtered face and house stimuli to assess the integrity of magnocellular and parvocellular pathways within the visual system. The magnocellular pathway is dominated by low spatial frequency (LSF) information and is faster than the parvocellular pathway, which processes high spatial frequency (HSF) information. This revealed an unusual pattern: M’s M170 was greater for HSF than LSF faces, whereas the opposite was evident in normal controls. In addition, M showed no difference in his M170 to HSF and LSF places whereas controls showed a greater response to HSF places than LSF places. We speculate that this atypical neural response to differing spatial frequencies reflects a mismatch in the information processing in these two pathways, resulting in M’s visual perseveration. Acknowledgements ANR and MAW are supported by the Australian Research Council (DP0984494 and DP0984494). Keywords: Visual perseveration, visual persistence, Magnetoencephalograhy, magnocellular pathway, Parvocellular pathway, M170 Conference: ACNS-2012 Australasian Cognitive Neuroscience Conference, Brisbane, Australia, 29 Nov - 2 Dec, 2012. Presentation Type: Oral Presentation Topic: Sensation and Perception Citation: Williams MA, Awasthi B, Sowman PF, Finkbeiner MS and Rich AN (2012). Atypical neural response to high and low spatial frequency stimuli in a rare case of visual perseveration. Conference Abstract: ACNS-2012 Australasian Cognitive Neuroscience Conference. doi: 10.3389/conf.fnhum.2012.208.00163 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 25 Oct 2012; Published Online: 17 Nov 2012. * Correspondence: Dr. Mark A Williams, Macquarie University, Cognitive Science, Sydney, Australia, mark.williams@mq.edu.au Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Mark A Williams Bhuvanesh Awasthi Paul F Sowman Matthew S Finkbeiner Anina N Rich Google Mark A Williams Bhuvanesh Awasthi Paul F Sowman Matthew S Finkbeiner Anina N Rich Google Scholar Mark A Williams Bhuvanesh Awasthi Paul F Sowman Matthew S Finkbeiner Anina N Rich PubMed Mark A Williams Bhuvanesh Awasthi Paul F Sowman Matthew S Finkbeiner Anina N Rich Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Surround suppression by high spatial frequency stimuli in the cat primary visual cortex

Surround suppression is a phenomenon whereby stimulation of the extraclassical receptive field suppressively modulates the visual responses of neurons in the primary visual cortex (V1) (also known as area 17). It is known that surround suppression tunes to spatial frequencies (SFs) that are much lower and broader than the frequencies to which the classical receptive field tunes. In this study, we tested the effects of varying SFs on surround suppression by using a circular sinusoidal grating patch that covered both the classical receptive field and the extraclassical receptive field. Using area-summation tuning curves, we found high-SF-tuned surround suppression in the cat V1. This high-SF-tuned surround suppression causes the SF tuning to shift to low SF for large stimuli. By simulating a model neuron lacking a suppressive surround mechanism, we confirmed that these preferred SF shifts do not occur in the absence of surround suppression. We surmise that the high-SF-tuned suppression, which shifts the preferred SF according to size, functionally contributes to the scale-invariant processing of visual images in V1.

Three-Dimensional Computer-Based Model for Analysis of the Endonasal Endoscopic Approach to the Midline Skull Base

Saccadic eye movements can drastically affect motion perception: during saccades, the stationary surround is swept rapidly across the retina and contrast sensitivity is suppressed. However, after saccades, contrast sensitivity is enhanced for color and high-spatial frequency stimuli and reflexive tracking movements known as ocular following responses (OFR) are enhanced in response to large field motion. Additionally, OFR and postsaccadic enhancement of neural activity in primate motion processing areas are well correlated. It is not yet known how this postsaccadic enhancement arises. Therefore, we tested if the enhancement can be explained by changes in the balance of centre-surround antagonism in motion processing, where spatial summation is favoured at low contrasts and surround suppression is favoured at high contrasts. We found motion perception was selectively enhanced immediately after saccades for high spatial frequency stimuli, consistent with previously reported selective postsaccadic enhancement of contrast sensitivity for flashed high spatial frequency stimuli. The observed enhancement was also associated with changes in spatial summation and suppression, as well as contrast facilitation and inhibition, suggesting that motion processing is augmented to maximise visual perception immediately after saccades. The results highlight that spatial and contrast properties of underlying neural mechanisms for motion processing can be affected by an antecedent saccade for highly detailed stimuli and are in line with studies that show behavioural and neuronal enhancement of motion processing in non-human primates.

Effects of spatial frequency and location of fearful faces on human amygdala activity

Facial emotion perception plays a fundamental role in interpersonal social interactions. Images of faces contain visual information at various spatial frequencies. The amygdala has previously been reported to be preferentially responsive to low-spatial frequency (LSF) rather than to high-spatial frequency (HSF) filtered images of faces presented at the center of the visual field. Furthermore, it has been proposed that the amygdala might be especially sensitive to affective stimuli in the periphery. In the present study we investigated the impact of spatial frequency and stimulus eccentricity on face processing in the human amygdala and fusiform gyrus using functional magnetic resonance imaging (fMRI). The spatial frequencies of pictures of fearful faces were filtered to produce images that retained only LSF or HSF information. Facial images were presented either in the left or right visual field at two different eccentricities. In contrast to previous findings, we found that the amygdala responds to LSF and HSF stimuli in a similar manner regardless of the location of the affective stimuli in the visual field. Furthermore, the fusiform gyrus did not show differential responses to spatial frequency filtered images of faces. Our findings argue against the view that LSF information plays a crucial role in the processing of facial expressions in the amygdala and of a higher sensitivity to affective stimuli in the periphery.