Contrast Perception Research Articles

Mechanical properties affect detectability of perceived texture contrast in heterogeneous food gels

This study investigated the influence of mechanical and physicochemical properties of semi-solid model foods on the detection and temporal perception of texture contrast. Gel-based model foods consisting of two layers were used to systematically vary mechanical contrast and physicochemical properties within bi-layer gels. Fracture stress (σF) and strain (εF) were modified by changing the concentration of various gelling agents (agar, к-carrageenan, and gelatine). The physicochemical properties of gels varied with respect to syneresis and melting behaviour depending on the type of gelling agent. The detection limit of perceived texture contrast of bi-layer gels was determined using ranking tests. Subjects ranked gels in order of increasing perceived heterogeneity as a measure of texture contrast. The detection limit of texture contrast varied between brittle and elastic gels and between soft (low σF) and hard (high σF) gels. In soft and brittle agar gels, heterogeneity was perceived already when the difference in fracture stress between layers was small (ΔσF ≥5 kPa). In soft and elastic gels (к-carrageenan, gelatine) and hard gels, heterogeneity was perceived only when the difference in fracture stress between the layers was large (ΔσF ≥12 kPa). The perceived heterogeneity intensity over time was investigated by time-intensity profiling. During mastication, gelatine gels were perceived for a longer period of time with a higher heterogeneity intensity than agar and к-carrageenan gels. We conclude that mainly mechanical properties of gels impact detectability of mechanical contrast as perceived texture contrast (heterogeneity), whereas a combination of mechanical and physicochemical properties influence the dynamic perception of heterogeneity over time.

Chromatic and achromatic visual fields in relation to choroidal thickness in patients with high myopia: A pilot study

To analyse the relationship between the choroidal thickness and the visual perception of patients with high myopia but without retinal damage. All patients underwent ophthalmic evaluation including a slit lamp examination and dilated ophthalmoscopy, subjective refraction, best corrected visual acuity, axial length, optical coherence tomography, contrast sensitivity function and sensitivity of the visual pathways. We included eleven eyes of subjects with high myopia. There are statistical correlations between choroidal thickness and almost all the contrast sensitivity values. The sensitivity of magnocellular and koniocellular pathways is the most affected, and the homogeneity of the sensibility of the magnocellular pathway depends on the choroidal thickness; when the thickness decreases, the sensitivity impairment extends from the center to the periphery of the visual field. Patients with high myopia without any fundus changes have visual impairments. We have found that choroidal thickness correlates with perceptual parameters such as contrast sensitivity or mean defect and pattern standard deviation of the visual fields of some visual pathways. Our study shows that the magnocellular and koniocellular pathways are the most affected, so that these patients have impairment in motion perception and blue-yellow contrast perception.

Retinex-Based Perceptual Contrast Enhancement in Images Using Luminance Adaptation

In this paper, we propose retinex-based perceptual contrast enhancement in images using luminance adaptation. Strong illumination causes the loss of local details in an image. We adopt luminance adaptation and multi-scale retinex (MSR) to successfully remove the illumination effect in an image while enhancing details. First, we estimate the illumination component in an image by adaptive smoothing and get luminance just-noticeable difference (JND) from it using luminance adaptation. Then, we calculate an illumination weakening factor from luminance JND and conduct MSR based on it to enhance details. Finally, we perform contrast enhancement using adaptive gamma correction with weighted distribution. Experimental results demonstrate that the proposed method successfully enhances details in an image while preventing over and under enhancement as well as outperforms state of the arts in terms of various quantitative measurements.

소규모 사무실 공간의 조명환경 변화에 대한 공간만족도 예측

This study examines the influence of lighting systems on the visual and spatial satisfaction for small office spaces. Two small office spaces were modeled using a software utilized for practical lighting designs. Direct and indirect lighting systems were applied to the space to provide a target illuminance of 650 lx. The modeled space were projected on a screen in a classroom and evaluated by 18 participants. Results indicate that the indirect lighting was effective to keep space bright and decorative. The indirect lighting contributed to sense the space spacious and mitigate the perception of contrast in space. The levels of psychological, visual and spatial satisfaction for space with the indirect lighting were superior to those under the direct lighting. Those sensations were mainly influenced by visual comfort, satisfaction with lighting, light distributions and illuminance levels.

Face Attractiveness versus Artistic Beauty in Art Portraits: A Behavioral Study.

From art portraits, the observer may derive at least two different hedonic values: The attractiveness of the depicted person and the artistic beauty of the image that relates to the way of presentation. We argue that attractiveness is a property that is predominantly driven by perceptual processes, while the perception of artistic beauty is based predominantly on cognitive processing. To test this hypothesis, we conducted two behavioral experiments. In a gist study (Experiment 1), we showed that ratings on attractiveness were higher after short-term presentation (50 ms) than after long-term presentation (3000 ms), while the opposite pattern was found for artistic beauty. In an experiment on perceptual contrast (Experiment 2), we showed that the perceptual contrast effect was stronger for attractiveness than for artistic beauty. These results are compatible with our hypothesis that appreciation of artistic beauty is cognitively modulated at least in part, while processing of attractiveness is predominantly driven perceptually. This dichotomy between cognitive and perceptual processing of different kinds of beauty suggests the participation of different neuronal mechanisms.

The influence of endogenous attention on contrast perception, contrast discrimination, and saccadic reaction time

Visual spatial attention has been shown to influence both contrast detection and suprathreshold contrast perception, as well as manual and saccadic reaction times (SRTs). Because SRTs are influenced also by stimulus contrast, we investigated if the enhancement of perceived contrast that accompanies attention could account for the shorter SRTs observed for attended targets locations. We conducted two dual-task experiments to assess psychophysical and oculomotor responses to non-foveal targets of various contrast for different spatial-attention-cueing conditions. Cues were either: valid, an arrow at fixation pointing in the direction of the upcoming target; invalid, an arrow pointing in a different direction from the target; or neutral, a small circle instead of an arrow. In both experiments, subjects were instructed to make a saccade to the location of a subsequent, briefly flashed target. In the first experiment, the psychophysical judgment was a two-alternative-forced-choice (2AFC) contrast-detection task, in which subjects reported whether the flashed target was at a near (3°) or far (6°) eccentricity. In the second experiment, the judgment was a contrast matching task, in which subjects reported whether the target’s contrast was higher or lower than a remembered standard contrast. The results exhibit a robust, ∼40–50 ms reduction of SRTs with a valid compared to an invalid cue. Cueing effects on contrast detection and matching were small and inconsistent across subjects. Hence, the observed decrease in SRTs could not be accounted for fully by an enhancement in the target’s effective contrast due to attention, as attended and unattended targets that were equally detectable or were perceived to have the same suprathreshold contrast showed substantial differences in SRT.

Introduction

Introduction

So Close Yet So Far Apart: Contrasting Climate Change Perceptions in Two “Neighboring” Coastal Communities on Aotearoa New Zealand’s Coromandel Peninsula

Coastal hazard risk, compounded by climate change, is escalating. Efforts to address this challenge are fraught and ‘success’ is elusive. We focus on this impasse and recommend ways to improve understanding, reduce risk and enable adaptation. Two Aotearoa New Zealand coastal communities, Mercury Bay and Kennedy Bay, on the Coromandel Peninsula, serve as case studies. Ethnographic fieldwork underpins this analysis. Despite close proximity, local perceptions are ‘worlds apart’. Poor understanding of climate change, and preoccupation with everyday issues, is commonplace. Moreover, there are countervailing community narratives. In Kennedy Bay, which is undeveloped and Māori, climate change is not a manifest concern. Local narratives are rooted in Māori culture and under the shadow of colonization, which shapes contemporary perceptions, practices and prospects. In Mercury Bay, a rapidly developing resort town, seashore property owners demand protection works—ignoring sea-level rise and privileging short-term private interests. Despite laudable regulatory provisions, static responses to dynamic risks prevail and proactive adaptation is absent. Recommendations are made to improve understanding about local cultural-social-ecological characteristics, climate change and adaption. Enabling leadership and capability-building are needed to institutionalize proactive adaptation. Strengthening Māori self-determination (rangatiratanga) and guardianship (kaitiakitanga), and local democracy, are key to mobilizing and sustaining community-based adaptation governance.

The relationship between contrast sensitivity and retinal nerve fiber layer thickness in patients with glaucoma.

To evaluate the correlation between contrast sensitivity (CS) and retinal nerve fiber layer (RNFL) in different areas of vision. This report is a sub-analysis of a prospective, observational cohort study investigating changes in performance-based assessment, vision-related quality of life, and clinical measures in patients with moderate to advanced glaucoma. The study included 161 participants with at least a 2-year history of glaucoma who underwent annual testing for 4years. Contrast sensitivity was measured using the Spaeth/Richman contrast sensitivity (SPARCS) test, while RNFL thickness (RNFLT) was measured using Cirrus optical coherence tomography (OCT). Statistical analyses were performed to determine correlations between CS and RNFLT; the correlations were calculated for each annual visit, totaling four correlation coefficients for each patient over the course of 4years. The SPARCS score in the left upper area of vision correlated the most strongly with the RNFLT of the inferior quadrant for both eyes at each annual visit, specifically in the seven o'clock sector for the left eye and the six o'clock sector for the right eye (p<0.05). There were no discernible trends for the correlations between the other areas of CS and RNFL quadrants or clock hours over the 4years of the study. Linear regression between the SPARCS total score and average RNFLT showed a significant direct correlation at each visit (p<0.01). Contrast sensitivity in the left upper area of vision for both eyes correlated most strongly with the thickness of the inferior quadrant of the RNFL. These fibers project to the temporal portion of the right occipital lobe, implying a potential center for contrast perception in this area. The longitudinal nature of the study suggests that CS may be a predictive tool for changes in RNFL in patients with glaucoma. Despite this finding, retinal damage and its relationship to CS was diffuse. In addition, SPARCS was shown to predict RNFLT. Further research is warranted to understand how CS can be used as a tool in the clinical setting.

Perception of global image contrast involves transparent spatial filtering and the integration and suppression of local contrasts (not RMS contrast).

When adjusting the contrast setting on a television set, we experience a perceptual change in the global image contrast. But how is that statistic computed? We addressed this using a contrast-matching task for checkerboard configurations of micro-patterns in which the contrasts and spatial spreads of two interdigitated components were controlled independently. When the patterns differed greatly in contrast, the higher contrast determined the perceived global contrast. Crucially, however, low contrast additions of one pattern to intermediate contrasts of the other caused a paradoxical reduction in the perceived global contrast. None of the following metrics/models predicted this: max, linear sum, average, energy, root mean squared (RMS), Legge and Foley. However, a nonlinear gain control model, derived from contrast detection and discrimination experiments, incorporating wide-field summation and suppression, did predict the results with no free parameters, but only when spatial filtering was removed. We conclude that our model describes fundamental processes in human contrast vision (the pattern of results was the same for expert and naive observers), but that above threshold—when contrast pedestals are clearly visible—vision's spatial filtering characteristics become transparent, tending towards those of a delta function prior to spatial summation. The global contrast statistic from our model is as easily derived as the RMS contrast of an image, and since it more closely relates to human perception, we suggest it be used as an image contrast metric in practical applications.

Long-Lasting Enhancement of Visual Perception with Repetitive Noninvasive Transcranial Direct Current Stimulation.

Understanding processes performed by an intact visual cortex as the basis for developing methods that enhance or restore visual perception is of great interest to both researchers and medical practitioners. Here, we explore whether contrast sensitivity, a main function of the primary visual cortex (V1), can be improved in healthy subjects by repetitive, noninvasive anodal transcranial direct current stimulation (tDCS). Contrast perception was measured via threshold perimetry directly before and after intervention (tDCS or sham stimulation) on each day over 5 consecutive days (24 subjects, double-blind study). tDCS improved contrast sensitivity from the second day onwards, with significant effects lasting 24 h. After the last stimulation on day 5, the anodal group showed a significantly greater improvement in contrast perception than the sham group (23 vs. 5%). We found significant long-term effects in only the central 2–4° of the visual field 4 weeks after the last stimulation. We suspect a combination of two factors contributes to these lasting effects. First, the V1 area that represents the central retina was located closer to the polarization electrode, resulting in higher current density. Second, the central visual field is represented by a larger cortical area relative to the peripheral visual field (cortical magnification). This is the first study showing that tDCS over V1 enhances contrast perception in healthy subjects for several weeks. This study contributes to the investigation of the causal relationship between the external modulation of neuronal membrane potential and behavior (in our case, visual perception). Because the vast majority of human studies only show temporary effects after single tDCS sessions targeting the visual system, our study underpins the potential for lasting effects of repetitive tDCS-induced modulation of neuronal excitability.

Perception of the Lexical Accent Contrast in One Variety of East Norwegian.

The perception of the lexical pitch accents was examined in the Trøndersk dialect of Norwegian. Based on a production study, a categorization of stimuli with manipulated pitch contours was conducted. The experiment tested which acoustic cues (height and alignment of fundamental frequency (F0) minimum, and alignment of F0 maximum and turning point from maximum to minimum) are necessary for the perception of the tonal contrast. The results are consistent with the production findings in that changes in all of the examined acoustic cues contributed to the shift in accent categorization. The later alignment of the main F0 landmarks (F0 maximum, F0 minimum and turning point from maximum to minimum) induced accent 2 identification. Raising F0 minimum height also led to more accent 2 responses. The analysis of the perception patterns furthermore revealed that the effect of a later alignment of F0 minimum was weak unless combined with a later alignment of the other F0 landmarks, or a higher F0 minimum level, all of which contributed to more accent 2 responses. These results indicate that accent 1 is characterized by an early fall, and accent 2 by a salient initial high tone. Implications of these findings for the phonological analysis of the tonal contrasts in the Trøndersk dialect are also discussed.

Canadian Raising in Chicagoland: The production and perception of a marginal contrast

In some North American English varieties the diphthong /aɪ/ has developed a distinctively higher nucleus before voiceless consonants and also before a flapped /t/. The phenomenon is known as Canadian Raising, as it was first described for Canadian English. We report on variation in the production and perception of this distinction in a group of female and male speakers from the Chicago area. We focus on the context before flapped /t/ and /d/. The production results show that there is a significant difference in the quality of both the nucleus and the offglide between these two contexts, albeit of a smaller magnitude than the difference observed before word-final voiceless and voiced consonants. In addition, we find a small difference in duration between diphthongs in the two pre-flap contexts. In perception, our subjects were only moderately successful in recognizing words in minimal pairs containing the target diphthong preceding a flap (as in writer vs rider), although with much higher than chance accuracy. A Quadratic Discriminant Analysis model classified the stimuli with substantially greater accuracy than our subjects. We conclude that in this English variety there is a contrast between a higher diphthong [ʌi] and a lower diphthong [aɪ], but this contrast is only marginal. This study contributes to our understanding of marginal contrasts in production and perception. The understanding of these contrasts has both theoretical and practical relevance.

Moving beyond the Western versus Asian culture distinction

PurposeThis study aims to analyze the joint effects of where a service failure occurs and who witnesses it, with a specific focus on Chinese consumers who have varying levels of acculturation.Design/methodology/approachA 4 × 2 × 2 between-subject factorial design was used, where social presence and the location of the service failure were manipulated and acculturation was measured. Data were collected in Australia and China to contrast perceptions and behavioral responses of Chinese – Australians and Mainland Chinese by drawing on samples of 224 and 264 respondents, respectively.FindingsResults showed significant differences in face, satisfaction and repeat purchase intention ratings following a service failure between Chinese – Australians and Mainland Chinese, as well as among Chinese – Australians with different acculturation strategies. Contrary to expectations, results established that where and with whom a service failure is experienced prominently affect consumer behavior regardless of the acculturation level.Practical implicationsAn understanding of the effect of acculturation on a service failure situation is crucial for businesses to successfully compete in a continuously globalized world where migration produces multicultural societies and short-term travel tends to significantly change demands on service provision.Originality/valueThis research presents one of the first studies that go beyond the traditional East/West consumer distinction in studying service failure. This study analyzes the effect of acculturation by itself and together with other variables of interest.

Retinal lateral inhibition revisited

Retinal lateral inhibition has long been known as the ‘contrast encoder’ and the relationship among retinal processing, lateral inhibition, and contrast perception has been discussed in the conventional scheme of difference-of-Gaussian (DoG). However, many studies argued that the classic DoG RF failed to explain contrast perception phenomena involving large spatial scale surface interaction (~1 deg). On the other hand, we recently showed that one of the neglected retinal features, wide-RF of retinal interneurons, explains how the visual system performs long-range interaction (Kim & Bertalmio, 2015). The long-range effect was previously explained by the multiscale DoG model (Blakeslee & McCourt, 1997) that proposes a varying spatial-frequency-bandwidth-channel processing. Here we show that the the retinal hierarchical center-surround processing architecture combined with interneurons of narrow and wide RFs accomplishes multi-channel-like results. We propose an update to the conventional view on lateral inhibition.

The power of a unimodal distribution in cue reweighting: Unimodality vs prediction error as signs of cue irrelevance

Maye & Gerken (2000) proposed that sound categories can be learned from probability distributions: a unimodal distribution suggests a single category, while a bimodal one suggests two contrasting ones. Research on distributional learning has focused on developing a contrast through exposure to a bimodal distribution. Here, we instead investigate how exposure to a unimodal distribution affects perception of a pre-existing multidimensional contrast (voicing, for which the primary cue is VOT). A total of 60 adult native English speakers were exposed to either bimodal or unimodal VOT distributions spanning the unaspirated/aspirated boundary (bear/pear). However, we paired acoustic stimuli with pictures of bears and pears independently of VOT in training. For each stimulus, participants were asked to guess the referent and received (random) feedback, generating an error signal that suggested VOT is no longer informative and should be downweighed. In this design, the bimodal distribution suggests the existence ...

Task differences do not impede overall learning when adapting to a novel sound

Lexically guided perceptual learning (LGPL) and second-language learning (L2) research seeks to understand how listeners adapt to novel speech sounds. In LGPL, listeners shift their perception of a native phonetic contrast in response to hearing an ambiguous token embedded in an unambiguous lexical context. In L2 tasks, often involve categorizing non-native sounds, usually with explicit feedback. In general, L2 learning is seen as more effortful and individually variable than LGPL. However, paradigms differ in terms of stimuli (native vs. non-native phonetic contrasts) as well as tasks (lexically-guided implicit feedback vs. explicit feedback). To test whether L2-type vs. LGPL-type tasks yield differences in learning, participants were trained using an L2-style task to shift their native boundary along an /s/ to /sh/ continuum. With feedback, participants categorized the midpoint token as one novel object, and an endpoint token (counterbalanced across subjects) as another novel object. After training, a boundary shift comparable to previous studies using the LGPL task was found, suggesting that explicit and lexically-guided feedback produce similar magnitude of learning. Despite this, participants in the L2-style task experienced lower accuracy and more variability in perception of the continuum endpoints, suggesting that task differences partially explain less consistency across individuals in L2 research.

A novel form of perceptual attunement: Context-dependent perception of a native contrast in 14-month-old infants

By the end of their first year of life, infants have become experts in discriminating the sounds of their native language, while they have lost the ability to discriminate non-native contrasts. This type of phonetic learning is referred to as perceptual attunement. In the present study, we investigated the emergence of a context-dependent form of perceptual attunement in infancy. Indeed, some native contrasts are not discriminated in certain phonological contexts by adults, due to the presence of a language-specific process that neutralizes the contrasts in those contexts. We used a mismatch design and recorded high-density Electroencephalography (EEG) in French-learning 14-month-olds. Our results show that similarly to French adults, infants fail to discriminate a native voicing contrast (e.g., [f] vs. [v]) when it occurs in a specific phonological context (e.g. [ofbe] vs. [ovbe], no mismatch response), while they successfully detected it in other phonological contexts (e.g., [ofne] vs. [ovne], mismatch response). The present results demonstrate for the first time that by the age of 14 months, infants’ phonetic learning does not only rely on the processing of individual sounds, but also takes into account in a language-specific manner the phonological contexts in which these sounds occur.

The Retina of Asian and African Elephants: Comparison of Newborn and Adult

Elephants are precocial mammals that are relatively mature as newborns and mobile shortly after birth. To determine whether the retina of newborn elephants is capable of supporting the mobility of elephant calves, we compared the retinal structures of 2 newborn elephants (1 African and 1 Asian) and 2 adult animals of both species by immunohistochemical and morphometric methods. For the first time, we present here a comprehensive qualitative and quantitative characterization of the cellular composition of the newborn and the adult retinas of 2 elephant species. We found that the retina of elephants is relatively mature at birth. All retinal layers were well discernible, and various retinal cell types were detected in the newborns, including Müller glial cells (expressing glutamine synthetase and cellular retinal binding protein; CRALBP), cone photoreceptors (expressing S-opsin or M/L-opsin), protein kinase Cα-expressing bipolar cells, tyrosine hydroxylase-, choline acetyltransferase (ChAT)-, calbindin-, and calretinin-expressing amacrine cells, and calbindin-expressing horizontal cells. The retina of newborn elephants contains discrete horizontal cells which coexpress ChAT, calbindin, and calretinin. While the overall structure of the retina is very similar between newborn and adult elephants, various parameters change after birth. The postnatal thickening of the retinal ganglion cell axons and the increase in ganglion cell soma size are explained by the increase in body size after birth, and the decreases in the densities of neuronal and glial cells are explained by the postnatal expansion of the retinal surface area. The expression of glutamine synthetase and CRALBP in the Müller cells of newborn elephants suggests that the cells are already capable of supporting the activities of photoreceptors and neurons. As a peculiarity, the elephant retina contains both normally located and displaced giant ganglion cells, with single cells reaching a diameter of more than 50 µm in adults and therefore being almost in the range of giant retinal ganglion cells found in aquatic mammals. Some of these ganglion cells are displaced into the inner nuclear layer, a unique feature of terrestrial mammals. For the first time, we describe here the occurrence of many bistratified rod bipolar cells in the elephant retina. These bistratified bipolar cells may improve nocturnal contrast perception in elephants given their arrhythmic lifestyle.

Describing contrast across scales

Due to its sensitive nature against illumination and noise distributions, contrast is not widely used for image description. On the contrary, the human perception of contrast along different spatial frequency bandwidths provides a powerful discriminator function that can be modeled in a robust manner against local illumination. Based upon this observation, a dense local contrast descriptor is proposed and its potential in different applications of computer vision is discussed. Extensive experiments reveal that this simple yet effective description performs well in comparison with state of the art image descriptors. We also show the importance of this description in multiresolution pansharpening framework.