Mid-range Spatial Frequencies Research Articles

Trypophobia an Unrevealed Truth: A Glance of Its Awareness and Prevalence in General Population of Pakistan

Background: Trypophobia is a psychological fear and has been described as a phobia to images with high-contrast energy at low and midrange spatial frequencies, such as holes and repetitive patterns. Method: This randomized study was conducted from September 2016 to March 2017 (n=214) through online surveys, visiting various university departments, interviewing common laymen and individuals from dissimilar families to approach maximum number of participants with less biasness. This was a useful survey for assessing the level of awareness and number of causalities in Pakistani population. Result: Results of current study show that there were few individuals diagnosed with trypophobia and were trying to get rid of it. Other individuals were either unknown or confused about this fear. Conclusion: We conclude that this study is beneficial for assessing presence of trypophobic fear in Pakistani population. Bangladesh Journal of Medical Science Vol. 22 No. 03 July’23 Page : 638-642

Effect of temporal frequency on habituation in migraine.

Individuals with migraine tend to experience discomfort when viewing flickering stimuli. It has been suggested that one of the characteristics of migraine is a lack of habituation to repetitive visual stimuli, although findings can be mixed. Previous work has typically used similar visual stimuli (chequerboard) and only one temporal frequency. This study systematically varied the spatial and temporal characteristics of the visual stimulus, using steady-state visual evoked potentials to assess the differences in amplitude between migraine and control group over consecutive blocks of stimulation. Twenty individuals with migraine and 18 control observers were asked to rate their visual discomfort after viewing sequences of flickering Gabor patches with a frequency of either 3 or 9 Hz across three different spatial frequencies (low 0.5 cpd; mid-range 3 cpd; high 12 cpd). Compared to the control group, the migraine group showed a reduction in SSVEP responses with increased exposure, suggesting habituation processes are intact at 3-Hz stimulation. However, at 9-Hz stimulation, there was evidence of increased responses with increasing exposure in the migraine group in particular, which might suggest a build-up of the response over repetitive presentations. Visual discomfort varied with spatial frequency, for both 3- and 9-Hz stimuli, the highest spatial frequencies were the least uncomfortable compared to the low- and mid-range spatial frequencies in both groups. This difference in SSVEP response behaviour, dependent on temporal frequency, is important to consider when researching the effects of repetitive visual stimulation in migraine and could give some indication of build-up of effects leading to aversion to visual stimuli.

Attenuated alpha oscillation and hyperresponsiveness reveals impaired perceptual learning in migraineurs

BackgroundAnomalous phantom visual perceptions coupled to an aversion and discomfort to some visual patterns (especially grating in mid-range spatial frequency) have been associated with the hyperresponsiveness in migraine patients. Previous literature has found fluctuations of alpha oscillation (8-14 Hz) over the visual cortex to be associated with the gating of the visual stream. In the current study, we examined whether alpha activity was differentially modulated in migraineurs in anticipation of an upcoming stimulus as well as post-stimulus periods.MethodsWe used EEG to examine the brain activity in a group of 28 migraineurs (17 with aura /11 without) and 29 non-migraineurs and compared their alpha power in the pre/post-stimulus period relative to the onset of stripped gratings.ResultsOverall, we found that migraineurs had significantly less alpha power prior to the onset of the stimulus relative to controls. Moreover, migraineurs had significantly greater post-stimulus alpha suppression (i.e event-related desynchronization) induced by the grating in 3 cycles per degree at the 2nd half of the experiment.ConclusionsThese findings, taken together, provide strong support for the presence of the hyperresponsiveness of the visual cortex of migraine sufferers. We speculate that it could be the consequence of impaired perceptual learning driven by the dysfunction of GABAergic inhibitory mechanism.

Object Clusters or Spectral Energy? Assessing the Relative Contributions of Image Phase and Amplitude Spectra to Trypophobia.

Trypophobia refers to the visual discomfort experienced by some people when viewing clustered patterns (e.g., clusters of holes). Trypophobic images deviate from the 1/f amplitude spectra typically characterizing natural images by containing excess energy at mid-range spatial frequencies. While recent work provides partial support for the idea of excess mid-range spatial frequency energy causing visual discomfort when viewing trypophobic images, a full factorial manipulation of image phase and amplitude spectra has yet to be conducted in order to determine whether the phase spectrum (sinusoidal waveform patterns that comprise image details like edge and texture elements) also plays a role in trypophobic discomfort. Here, we independently manipulated the phase and amplitude spectra of 31 Trypophobic images using a standard Fast Fourier Transform (FFT). Participants rated the four different versions of each image for levels of visual comfort, and completed the Trypophobia Questionnaire (TQ). Images having the original phase spectra intact (with either original or 1/f amplitude) explained the most variance in comfort ratings and were rated lowest in comfort. However, images with the original amplitude spectra but scrambled phase spectra were rated higher in comfort, with a smaller amount of variance in comfort attributed to the amplitude spectrum. Participant TQ scores correlated with comfort ratings only for images having the original phase spectra intact. There was no correlation between TQ scores and comfort levels when participants viewed the original amplitude / phase-scrambled images. Taken together, the present findings show that the phase spectrum of trypophobic images, which determines the pattern of small clusters of objects, plays a much larger role than the amplitude spectrum in determining visual discomfort.

Time course of spatial frequency integration in face perception: An ERP study

Face perception is based on the processing and integration of multiple spatial frequency (SF) ranges. However, the temporal dynamics of SF integration to form an early face representation in the human brain is still a matter of debate. To address this issue, we recorded event-related potentials (ERPs) during the presentation of spatial frequency-manipulated facial images. Twenty-six participants performed a gender discrimination task on non-filtered, low-, high-, and band-pass filtered face images, corresponding, respectively, to the full range, spatial frequencies up to 8 cycles/image, above 32 cycles/image, and from 8 to 16 cycles/image. Behaviorally, the task related-performance was more accurate and faster for non-filtered (NF) and mid-range SF (MSF) than for low SF (LSF) and high SF (HSF) stimuli. At both behavioral and electrophysiological levels, response to MSF contained in faces did not differ from the responses to full spectrum non-filtered (NF) facial images. In ERPs, LSF facial images evoked the largest P1 amplitude while HSF facial images evoked the largest N170 amplitude compared with the other three conditions. Since LSFs and HSFs would transmit global and local information respectively, our observations lend further support to the “coarse-to-fine” processing theory of faces. Furthermore, they offer original evidence of the effectiveness and adequacy of the mid-range spatial frequency in face perception. Possible theoretical interpretations of our findings are discussed.

Trypophobic Discomfort is Spatial-Frequency Dependent.

Clusters of holes, such as those in a lotus seedpod, induce trypophobic discomfort. Previous research has demonstrated that high-contrast energy at midrange spatial frequencies in images causes trypophobic discomfort. The present study examined the effects on discomfort of eliminating various spatial frequency components from the images to reveal how each spatial frequency contributes to the discomfort. Experiment 1 showed that eliminating midrange spatial frequencies did not affect trypophobic discomfort, while Experiment 2 revealed that images of holes that consisted of only high-spatial frequencies evoked less discomfort than other images and that images containing only low or midrange spatial frequencies induced as much trypophobic discomfort as did the original images. Finally, Experiment 3 found that participants with a high level of the trypophobic trait experienced stronger discomfort from the original images and the images containing only low or midrange spatial frequencies than participants with a low level of the trypophobic trait. Our findings thus suggest that trypophobic discomfort can be induced by middle and low spatial frequencies.

School-age children's neural sensitivity to horizontal orientation energy in faces.

Face processing mechanisms are tuned to specific low-level features including mid-range spatial frequencies and horizontal orientation energy. Behaviorally, adult observers are more effective at face recognition tasks when these information channels are available. Neural responses to face images also reflect these information biases: Face-sensitive ERP components respond preferentially to face images that contain horizontal orientation energy. How does neural tuning of face representations to horizontal information develop? Behavioral results show that this information bias increases over time such that younger children have a reduced bias favoring horizontally-filtered faces that increases with age. In the present study, we chose to investigate how neural sensitivity to these low-level features develops in the same age range, using ERP as a means of studying children and adults. Specifically, we examined how both face-sensitive ERP components (the P100 and N170) changed their responses to faces and non-faces as a function of age and orientation energy. Briefly, we found that the latency of the P100 and N170 component across age groups was consistent with the gradual emergence of a bias favoring horizontal orientation energy during middle childhood. The amplitude of the N170 component, however, exhibited a more complicated developmental profile that does not easily map onto previous behavioral results obtained from children in the same age ranges.

Active Vision: Dynamic Reformatting of Visual Information by the Saccade-Drift Cycle

Visual processing depends on rapid parsing of global features followed by analysis of fine detail. A new study suggests that this transformation is enabled by a cycle of saccades and fixational drifts, which reformat visual input to match the spatiotemporal sensitivity of fast and slow neuronal pathways.

Steady-state VEP responses to uncomfortable stimuli.

Periodic stimuli, such as op-art, can evoke a range of aversive sensations included in the term visual discomfort. Illusory motion effects are elicited by fixational eye movements, but the cortex might also contribute to effects of discomfort. To investigate this possibility, steady-state visually evoked responses (SSVEPs) to contrast-matched op-art-based stimuli were measured at the same time as discomfort judgements. On average, discomfort reduced with increasing spatial frequency of the pattern. In contrast, the peak amplitude of the SSVEP response was around the midrange spatial frequencies. Like the discomfort judgements, SSVEP responses to the highest spatial frequencies were lowest amplitude, but the relationship breaks down between discomfort and SSVEP for the lower spatial frequency stimuli. This was not explicable by gross eye movements as measured using the facial electrodes. There was a weak relationship between the peak SSVEP responses and discomfort judgements for some stimuli, suggesting that discomfort can be explained in part by electrophysiological responses measured at the level of the cortex. However, there is a breakdown of this relationship in the case of lower spatial frequency stimuli, which remains unexplained.

Assessment of trypophobia and an analysis of its visual precipitation.

We developed and validated a symptom scale that can be used to identify "trypophobia", in which individuals experience aversion induced by images of clusters of circular objects. The trypophobia questionnaire (TQ) was based on reports of various symptom types, but it nevertheless demonstrated a single construct, with high internal consistency and test-retest reliability. The TQ scores predicted discomfort from trypophobic images, but not neutral or unpleasant images, and did not correlate with anxiety. Using image filtering, we also reduced the excess energy at midrange spatial frequencies associated with both trypophobic and uncomfortable images. Relative to unfiltered trypophobic images, the discomfort from filtered images experienced by observers with high TQ scores was less than that experienced with control images and by observers with low TQ scores. Furthermore, we found that clusters of concave objects (holes) did not induce significantly more discomfort than clusters of convex objects (bumps), suggesting that trypophobia involves images with particular spectral profile rather than clusters of holes per se.

A face detection bias for horizontal orientations develops in middle childhood.

Faces are complex stimuli that can be described via intuitive facial features like the eyes, nose, and mouth, “configural” features like the distances between facial landmarks, and features that correspond to computations performed in the early visual system (e.g., oriented edges). With regard to this latter category of descriptors, adult face recognition relies disproportionately on information in specific spatial frequency and orientation bands: many recognition tasks are performed more accurately when adults have access to mid-range spatial frequencies (8–16 cycles/face) and horizontal orientations (Dakin and Watt, 2009). In the current study, we examined how this information bias develops in middle childhood. We recruited children between the ages of 5–10 years-old to participate in a simple categorization task that required them to label images according to whether they depicted a face or a house. Critically, children were presented with face and house images comprised either of primarily horizontal orientation energy, primarily vertical orientation energy, or both horizontal and vertical orientation energy. We predicted that any bias favoring horizontal information over vertical should be more evident in faces than in houses, and also that older children would be more likely to show such a bias than younger children. We designed our categorization task to be sufficiently easy that children would perform at near-ceiling accuracy levels, but with variation in response times that would reflect how they rely on different orientations as a function of age and object category. We found that horizontal bias for face detection (but not house detection) correlated significantly with age, suggesting an emergent category-specific bias for horizontal orientation energy that develops during middle childhood. These results thus suggest that the tuning of high-level recognition to specific low-level visual features takes place over several years of visual development.

Fear of Holes

Phobias are usually described as irrational and persistent fears of certain objects or situations, and causes of such fears are difficult to identify. We describe an unusual but common phobia (trypophobia), hitherto unreported in the scientific literature, in which sufferers are averse to images of holes. We performed a spectral analysis on a variety of images that induce trypophobia and found that the stimuli had a spectral composition typically associated with uncomfortable visual images, namely, high-contrast energy at midrange spatial frequencies. Critically, we found that a range of potentially dangerous animals also possess this spectral characteristic. We argue that although sufferers are not conscious of the association, the phobia arises in part because the inducing stimuli share basic visual characteristics with dangerous organisms, characteristics that are low level and easily computed, and therefore facilitate a rapid nonconscious response.

Auditory rhythms are systemically associated with spatial-frequency and density information in visual scenes

A variety of perceptual correspondences between auditory and visual features have been reported, but few studies have investigated how rhythm, an auditory feature defined purely by dynamics relevant to speech and music, interacts with visual features. Here, we demonstrate a novel crossmodal association between auditory rhythm and visual clutter. Participants were shown a variety of visual scenes from diverse categories and asked to report the auditory rhythm that perceptually matched each scene by adjusting the rate of amplitude modulation (AM) of a sound. Participants matched each scene to a specific AM rate with surprising consistency. A spatial-frequency analysis showed that scenes with greater contrast energy in midrange spatial frequencies were matched to faster AM rates. Bandpass-filtering the scenes indicated that greater contrast energy in this spatial-frequency range was associated with an abundance of object boundaries and contours, suggesting that participants matched more cluttered scenes to faster AM rates. Consistent with this hypothesis, AM-rate matches were strongly correlated with perceived clutter. Additional results indicated that both AM-rate matches and perceived clutter depend on object-based (cycles per object) rather than retinal (cycles per degree of visual angle) spatial frequency. Taken together, these results suggest a systematic crossmodal association between auditory rhythm, representing density in the temporal domain, and visual clutter, representing object-based density in the spatial domain. This association may allow for the use of auditory rhythm to influence how visual clutter is perceived and attended.

Visual search performance of patients with vision impairment: effect of JPEG image enhancement

To measure natural image search performance in patients with central vision impairment. To evaluate the performance effect for a JPEG based image enhancement technique using the visual search task. One hundred and fifty JPEG images were presented on a touch screen monitor in either an enhanced or original version to 19 patients (visual acuity 0.4-1.2 logMAR, 6/15 to 6/90, 20/50 to 20/300) and seven normally sighted controls (visual acuity -0.12 to 0.1 logMAR, 6/4.5 to 6/7.5, 20/15 to 20/25). Each image fell into one of three categories: faces, indoors, and collections. The enhancement was realized by moderately boosting a mid-range spatial frequency band in the discrete cosine transform (DCT) coefficients of the image luminance component. Participants pointed to an object in a picture that matched a given target displayed at the upper-left corner of the monitor. Search performance was quantified by the percentage of correct responses, the median search time of correct responses, and an 'integrated performance' measure - the area under the curve of cumulative correct response rate over search time. Patients were able to perform the search tasks but their performance was substantially worse than the controls. Search performances for the three image categories were significantly different (p <= 0.001) for all the participants, with searching for faces being the most difficult. When search time and correct response were analyzed separately, the effect of enhancement led to increase in one measure but decrease in another for many patients. Using the integrated performance, it was found that search performance declined with decrease in acuity (p = 0.005). An improvement with enhancement was found mainly for the patients whose acuity ranged from 0.4 to 0.8 logMAR (6/15 to 6/38, 20/50 to 20/125). Enhancement conferred a small but significant improvement in integrated performance for indoor and collection images (p = 0.025) in the patients. Search performance for natural images can be measured in patients with impaired vision to evaluate the effect of image enhancement. Patients with moderate vision loss might benefit from the moderate level of enhancement used here.

Evidence for elevated cortical hyperexcitability and its association with out-of-body experiences in the non-clinical population: New findings from a pattern-glare task

Individuals with no history of neurological or psychiatric illness can report hallucinatory Out-of-Body Experiences (OBEs) and display elevated scores on measures of temporal-lobe dysfunction (Braithwaite et al., 2011). However, all previous investigations of such biases in non-clinical populations are based on indirect questionnaire measures. Here we present the first empirical investigation that a non-clinical OBE group is subject to pattern-glare, possibly as a result of cortical hyperexcitability (Wilkins et al., 1984). Fifty-nine students at the University of Birmingham viewed a series of square-wave gratings with spatial frequencies of approximately .7, 3 and 11 cycles-per-degree, both black/white and of contrasting colours. The illusions and discomfort reported when viewing gratings with mid-range spatial frequency have been hypothesized to reflect cortical hyperexcitability (Wilkins, 1995; Huang et al., 2003). Participants also completed the Cardiff Anomalous Perception Scale (CAPS: Bell et al., 2006) which included experiential measures of disruptions in ‘Temporal-lobe Experience’. Participants who reported OBEs also reported significantly more visual illusions/distortions and significantly greater discomfort as a result of viewing the mid-frequency gratings. There were no such differences with respect to gratings with relatively lower or higher spatial frequency. The OBE group also produced significantly elevated scores on the CAPS measures of Temporal-lobe Experience, relative to controls. Collectively, the results are consistent with there being a neural ‘vulnerability’ in the cortices of individuals pre-disposed to some hallucinations, even in the non-clinical population.

Perceived time is spatial frequency dependent

We investigated whether changes in low-level image characteristics, in this case spatial frequency, were capable of generating a well-known expansion in the perceived duration of an infrequent “oddball” stimulus relative to a repeatedly-presented “standard” stimulus. Our standard and oddball stimuli were Gabor patches that differed from each other in spatial frequency by two octaves. All stimuli were equated for visibility. Rather than the expected “subjective time expansion” found in previous studies, we obtained an equal and opposite expansion or contraction of perceived time dependent upon the spatial frequency relationship of the standard and oddball stimulus. Subsequent experiments using equi-visible stimuli reveal that mid-range spatial frequencies (ca. 2c/deg) are consistently perceived as having longer durations than low (0.5c/deg) or high (8c/deg) spatial frequencies, despite having the same physical duration. Rather than forming a fixed proportion of baseline duration, this bias is constant in additive terms and implicates systematic variations in visual persistence across spatial frequency. Our results have implications for the widely cited finding that auditory stimuli are judged to be longer in duration than visual stimuli.

Optical Characterization of Bangerter Foils

Optical penalization is emerging as an alternative to patching for the treatment of amblyopia. Bangerter foils offer a form of optical penalization that is distinctly different from standard techniques making use of atropine or spectacle lens manipulation, or both, to produce defocus. The authors examined the optical properties of Bangerter foils and compared them with the effect of defocus. Bangerter foils were evaluated on an optical bench to calculate point spread and modulation transfer functions. Retinal images through the foils were also simulated and qualitatively compared with those with defocus and Gaussian blur. Subjective visual acuity and contrast sensitivity were compared in two subjects wearing spectacles with foils and with simple defocus. The optical characteristics of the Bangerter foils do not correspond well with their labeled density designation. Bangerter foils and defocus affect the modulation transfer function similarly, with more attenuation of mid-range spatial frequencies than low spatial frequencies. However, Bangerter foils do not exhibit spurious resolution and phase shifts, as does defocus. The blur resulting from Bangerter filters is qualitatively different from defocus. Whether this difference is of any consequence when these two methods of optical penalization are used for amblyopia treatment remains to be investigated.

Contrast sensitivity after implantation of toric iris-claw lenses in phakic eyes

Purpose: To evaluate the change in contrast sensitivity after implantation of the Verisyse toric phakic intraocular lens (IOL) (AMO) for the correction of myopia with astigmatism. Setting: Department of Ophthalmology, Johannes Gutenberg-University, Mainz, Germany. Methods: Eighteen eyes had implantation of an iris-supported toric phakic IOL to correct myopia with astigmatism. The mean preoperative spherical equivalent was −12.65 diopters ± 3.6 (SD). The contrast sensitivity with best spectacle correction was determined before surgery and 3 months after surgery using the CSV-1000 HGT instrument (Vector Vision Inc.). Results: Three months after IOL implantation, the mean contrast sensitivity had significantly increased from preoperatively at midrange spatial frequencies from 3.2 to 4.4 (6 cycles per degree [cpd]; P = .033) and from 2.4 to 3.7 (12 cpd; P = .032). The differences at spatial frequencies of 3 cpd and 18 cpd were not statistically significant ( P = .59 and P = .086, respectively). Conclusions: Implantation of the Verisyse toric iris-claw lens in phakic eyes to correct high or moderate myopia with astigmatism has the potential to improve contrast vision. The mean contrast sensitivity increased considerably at all spatial frequencies compared with preoperative levels.

Topographic change in the central macula coupled with contrast sensitivity loss in diabetic pregnancy.

To study macular topography and contrast sensitivity (CS) in diabetic and nondiabetic women during pregnancy and post partum. A prospective study of 46 pregnant women with insulin-dependent diabetes and 11 nondiabetic pregnant controls. Macular surface topography was analyzed by Heidelberg Retinal Tomograph. Volume above the reference plane (VARP) was measured with 1.0-, 1.5-, 2.0-, and 3.0-mm-diameter circles. CS was measured with the Vistech 6500 Contrast Test System. The diabetic women had greater VARP than the controls measured with the 1.5-mm diameter circle. In diabetic women, the mean VARP was 0.084+/-0.064 mm(3) (mean +/- SD) in the first trimester, 0.080 +/- 0.056 mm(3) in the third trimester, and 0.087 +/- 0.067 mm(3) 3 months post partum compared with the values of 0.069+/-0.043, 0.054+/-0.024, and 0.036+/-0.020 mm(3) in the controls ( P=0.036 between groups). In diabetic women requiring laser treatment, the difference from controls was more significant ( P<0.001). CS at 3 cpd and 6.0 cpd was lower in diabetic women than in controls throughout pregnancy and post partum ( P=0.012 and P=0.043). A statistically significant negative correlation appeared between macular topography and CS during the third trimester; between cpd 6 and VARP 1.5 mm ( r=-0.471, P=0.001), and between cpd 6 and VARP 2.0 mm ( r=-0.446, P=0.002). In the diabetic women, especially in those with clear progression of retinopathy during pregnancy and post-partum, the macula seemed to be slightly more elevated than in the controls, and CS was lower at mid-range spatial frequencies. CS loss in the diabetic women correlated with macular elevation during the third trimester.

Visual sensitivity in the presence of a patterned background.

The sensitivity of the visual system depends on ambient illumination: Sensitivity is reduced in the presence of a bright, uniform background. We asked how sensitivity is adjusted when the background is spatially detailed and therefore contains both luminance peaks and troughs in the neighborhood of a foreground object. A test flash was superimposed on a static sinusoidal grating. As the grating's spatial frequency increased, sensitivity for flash detection declined, regardless of whether the flash was superimposed on a peak or a trough of the grating. We studied the mechanisms underlying this loss of sensitivity by delivering the test stimulus through one eye and the background through the other. The conclusion is that three mechanisms are involved. Luminance adaptation and a masking process adjust sensitivity at low- and mid-range spatial frequencies, respectively. The third mechanism, a contrast gain control, is localized (it occurs at spatial frequencies approaching the limit for resolution) and fast (complete in half a second), and it results from early processing in the visual pathway (it is absent during dichoptic viewing). This local adjustment of sensitivity may help to protect the clarity of even the smallest details in the visual scene.