The speed of sight: Individual variation in critical flicker fusion thresholds.

The critical flicker fusion threshold is a psychophysical measure commonly used to quantify visual temporal resolution; the fastest rate at which a visual system can discriminate visual signals. Critical flicker fusion thresholds vary substantially among species, reflecting different ecological niches and demands. However, it is unclear how much variation exists in flicker fusion thresholds between healthy individuals of the same species, or how stable this attribute is over time within individuals. In this study, we assessed both inter- and intra-individual variation in critical flicker fusion thresholds in a cohort of healthy human participants within a specific age range, using two common psychophysical methods and three different measurements during each session. The resulting thresholds for each method were highly correlated. We found a between-participant maximum difference of roughly 30 Hz in flicker fusion thresholds and we estimated a 95% prediction interval of 21 Hz. We used random-effects models to compare between- and within-participant variance and found that approximately 80% of variance was due to between-individual differences, and about 10% of the variance originated from within-individual differences over three sessions. Within-individual thresholds did not differ significantly between the three sessions in males, but did in females (P<0.001 for two methods and P<0.05 for one method), indicating that critical flicker fusion thresholds may be more variable in females than in males.

Improving the robustness of the Sequentially Optimized Reconstruction Strategy (SORS) for visual field testing.

Perimetry, or visual field test, estimates differential light sensitivity thresholds across many locations in the visual field (e.g., 54 locations in the 24-2 grid). Recent developments have shown that an entire visual field may be relatively accurately reconstructed from measurements of a subset of these locations using a linear regression model. Here, we show that incorporating a dimensionality reduction layer can improve the robustness of this reconstruction. Specifically, we propose to use principal component analysis to transform the training dataset to a lower dimensional representation and then use this representation to reconstruct the visual field. We named our new reconstruction method the transformed-target principal component regression (TTPCR). When trained on a large dataset, our new method yielded results comparable with the original linear regression method, demonstrating that there is no underfitting associated with parameter reduction. However, when trained on a small dataset, our new method used on average 22% fewer trials to reach the same error. Our results suggest that dimensionality reduction techniques can improve the robustness of visual field testing reconstruction algorithms.

Factors influencing olfactory function in an adult general population sample: the CHRIS study.

The sense of smell allows for the assessment of the chemical composition of volatiles in our environment. Different factors are associated with reduced olfactory function, including age, sex, as well as health and lifestyle conditions. However, most studies that aimed at identifying the variables that drive olfactory function in the population suffered from methodological weaknesses in study designs and participant selection, such as the inclusion of convenience sample or only of certain age groups, or recruitment biases. We aimed to overcome these issues by investigating the Cooperative Health Research in South Tyrol (CHRIS) cohort, a population-based cohort, by using a validated odor identification test. Specifically, we hypothesized that a series of medical, demographic and lifestyle variables is associated with odor identification abilities. In addition, our goal was to provide clinicians and researchers with normative values for the Sniffin' Sticks identification set, after exclusion of individuals with impaired nasal patency. We included 6,944 participants without acute nasal obstruction and assessed several biological, social, and medical parameters. A basic model determined that age, sex, years of education, and smoking status together explained roughly 13% of the total variance in the data. We further observed that variables related to medical (positive screening for cognitive impairment and for Parkinson's disease, history of skull fracture, stage 2 hypertension) and lifestyle (alcohol abstinence) conditions had a negative effect on odor identification scores. Finally, we provide clinicians with normative values for both versions of the Sniffin' Sticks odor identification test, i.e. with 16 items and with 12 items.

An observational study of olfactory functions in total laryngectomees.

OBJECTIVE: To evaluate the olfactory acuity and quality of life in patients who have undergone total laryngectomy. The study also aims to identify any specific patient-related risk factors linked to worse olfactory outcomes. METHODS: This is a prospective cross-sectional study conducted at the University Malaya Medical Centre. A total of 30 patients who have undergone total laryngectomy were assessed objectively using the Sniffin' Sticks test and compared against normal age-matched Malaysians. Subsequently, they also filled out the modified Questionnaire on Olfactory Disorders. Correlations of patient demographics, disease and treatment variables against olfactory outcomes were conducted. RESULTS: All subjects suffered olfactory impairment, with 66.7% of them being anosmic after total laryngectomy. The Sniffin' Sticks test demonstrated a statistically significant difference between laryngectomees and the normal age-matched Malaysian population in all three subtests for odor threshold, discrimination and identification. 37% of patients developed olfactory adaptive methods, which resulted in higher olfactory scores and a better quality of life. There were no patient demographics, disease or treatment variables associated with a poorer olfactory outcome identified. CONCLUSION: Olfactory impairment should not be overlooked among patients after total laryngectomy. Although as many as a third of patients developed some sort of olfactory adaptive behavior, early rehabilitation should be integrated into the multidisciplinary rehabilitation program after total laryngectomy.

Effect of the rs2821557 Polymorphism of the Human Kv1.3 Gene on Olfactory Function and BMI in Different Age Groups.

The sense of smell plays an important role in influencing the eating habits of individuals and consequently, their body weight, and its impairment has been associated with modified eating behaviors and malnutrition problems. The inter-individual variability of olfactory function depends on several factors, including genetic and physiological ones. In this study, we evaluated the role of the Kv1.3 channel genotype and age, as well as their mutual relationships, on the olfactory function and BMI of individuals divided into young, adult and elderly groups. We assessed olfactory performance in 112 healthy individuals (young n = 39, adult n = 36, elderly n = 37) based on their TDI olfactory score obtained through the Sniffin' Sticks test and their BMI. Participants were genotyped for the rs2821557 polymorphism of the human gene encoding Kv1.3 channels, the minor C allele of which was associated with a decreased sense of smell and higher BMIs compared to the major T allele. The results show that TT homozygous subjects obtained higher TDI olfactory scores and showed lower BMIs than CC homozygous subjects, in all age groups considered. Furthermore, the positive effect of the T allele on olfactory function and BMI decreased with increasing age. The contribution of the genetic factor is less evident with advancing age, while the importance of the age factor is compensated for by genetics. These results show that genetic and physiological factors such as age act to balance each other.

Motion-Acuity Test for Visual Field Acuity Measurement with Motion-Defined Shapes.

The standard visual acuity measurements rely on stationary stimuli, either letters (Snellen charts), vertical lines (vernier acuity) or grating charts, processed by those regions of the visual system most sensitive to the stationary stimulation, receiving visual input from the central part of the visual field. Here, an acuity measurement is proposed based on discrimination of simple shapes, that are defined by motion of the dots in the random dot kinematograms (RDK) processed by visual regions sensitive to motion stimulation and receiving input also from the peripheral visual field. In the motion-acuity test, participants are asked to distinguish between a circle and an ellipse, with matching surfaces, built from RDKs, and separated from the background RDK either by coherence, direction, or velocity of dots. The acuity measurement is based on ellipse detection, which with every correct response becomes more circular until reaching the acuity threshold. The motion-acuity test can be presented in negative contrast (black dots on white background) or in positive contrast (white dots on black background). The motion defined shapes are located centrally within 8 visual degrees and are surrounded by RDK background. To test the influence of visual peripheries on centrally measured acuity, a mechanical narrowing of the visual field to 10 degrees is proposed, using opaque goggles with centrally located holes. This easy and replicable narrowing system is suitable for MRI protocols, allowing further investigations of the functions of the peripheral visual input. Here, a simple measurement of shape and motion perception simultaneously is proposed. This straightforward test assesses vision impairments depending on the central and peripheral visual field inputs. The proposed motion-acuity test advances the capability of standard tests to reveal spare or even strengthened vision functions in patients with injured visual system, that until now remained undetected.

Genetic Factors Associated with the Development of Neuropathy in Type 2 Diabetes.

Neuropathy is a serious and frequent complication of type 2 diabetes (T2DM). This study was carried out to search for genetic factors associated with the development of diabetic neuropathy by whole exome sequencing. For this study, 24 patients with long-term type 2 diabetes with neuropathy and 24 without underwent detailed neurological assessment and whole exome sequencing. Cardiovascular autonomic function was evaluated by cardiovascular reflex tests. Heart rate variability was measured by the triangle index. Sensory nerve function was estimated by Neurometer and Medoc devices. Neuropathic symptoms were characterized by the neuropathy total symptom score (NTSS). Whole exome sequencing (WES) was performed on a Thermo Ion GeneStudio S5 system determining the coding sequences of approximately 32,000 genes comprising 50 million base pairs. Variants were detected by Ion Reporter software and annotated using ANNOVAR, integrating database information from dbSNP, ClinVar, gnomAD, and OMIM. Integrative genomics viewer (IGV) was used for visualization of the mapped reads. We have identified genetic variants that were significantly associated with increased (22-49-fold) risk of neuropathy (rs2032930 and rs2032931 of recQ-mediated genome instability protein 2 (RMI2) gene), rs604349 of myosin binding protein H like (MYBPHL) gene and with reduced (0.07-0.08-fold) risk (rs917778 of multivesicular body subunit 12B (MVB12B) and rs2234753 of retinoic acid X receptor alpha (RXRA) genes). The rs2032930 showed a significant correlation with current perception thresholds measured at 5 Hz and 250 Hz for n. medianus (p = 0.042 and p = 0.003, respectively) and at 5 Hz for n. peroneus (p = 0.037), as well as the deep breath test (p = 0.022) and the NTSS (p = 0.023). The rs2032931 was associated with current perception thresholds (p = 0.003 and p = 0.037, respectively), deep breath test (p = 0.022), and NTSS (p = 0.023). The rs604349 correlated with values measured at 2000 (p = 0.049), 250 (p = 0.018), and 5 Hz (p = 0.005) for n. medianus, as well as warm perception threshold measured by Medoc device (p = 0.042). The rs2234753 showed correlations with a current perception threshold measured at 2000 Hz for n. medianus (p = 0.020), deep breath test (p = 0.040), and NTSS (p = 0.003). There was a significant relationship between rs91778 and cold perception threshold (p = 0.013). In our study, genetic variants have been identified that may have an impact on the risk of neuropathy developing in type 2 diabetic patients. These results could open up new opportunities for early preventive measures and might provide targets for new drug developments in the future.

Quantifying sensory thresholds along the migraine cycle: An exploratory longitudinal study.

BACKGROUND: To date, a number of studies on migraine have cross-sectionally evaluated sensory sensitivity with aversion thresholds/scores along the migraine cycle, reporting a decreased tolerance to sensory stimuli in different sensory modalities. Our hypothesis was that patients with migraine would exhibit heightened sensitivity to sound, light, touch and smell on days where they reported greater headache intensity. METHODS: This is an exploratory, longitudinal study, carried out over the course of 27 days. Aversion thresholds or scores to sound, light, touch and smell were quantified in six patients with migraine (11.33 ± 6.53 headache days/month). RESULTS: Patients reported an increased sensitivity to light (padj = 0.0297), touch (padj = 0.0077), and smell (padj = 0.0201) on days with higher headache intensity. However, a greater sensitivity to sound on days with higher headache intensity was only reported when anxiety levels were high (padj = 1.4e-06). Interestingly, variable levels of tolerance to bothersome light over time can also influence the correlation between light sensitivity and headache intensity (padj = 1.4e-06). CONCLUSIONS: Based on the present findings, future longitudinal studies evaluating sensory threshold changes along the migraine cycle in patients with migraine should account for the increased tolerance to bothersome light over time as well as the effect of anxiety on auditory sensitivity.

On the mechanics of monofilaments used in touch sensory perception.

The buckling of a slender monofilament is a standard clinical method used to assess touch sensory perception, with specific applications to somatosensory impairment in patients after a stroke, detecting carpal tunnel syndrome, and as a prognosis tool for diabetic peripheral neuropathy. The basis of this approach is the Semmes-Weinstein monofilament, which comprises a calibrated set of thin, polycarbonate rods with different diameters. Application of a monofilament onto the surface of the skin with increasing pressure causes the rod to buckle. That is, at a specific force of pushing down on the far end, the monofilament suddenly bows out sidewards - the buckling load. The ability of a patient to detect increasingly finer monofilament buckling (pressure threshold) is then used to assess sensory deterioration. This paper addresses the underlying mechanics of the buckling process. Despite the accuracy and repeatability problems that have been reported in the literature, and the necessarily subjective aspects of sensory physiology, the mathematical modeling of the monofilament buckling is unambiguous and provides some fundamental insight into the parameters that underlie this approach.

Bi-Manual Sensory Discrimination: A Kinesthetic Study.

The ability of humans to perceive and differentiate kinesthetic sensory information significantly influences our daily activities and motor control. This study examines the impact of asynchronous bi-manual discrimination tasks compared to uni-manual discrimination tasks on kinesthetic perception. Our study aims to reveal the relationship between kinesthetic perception of haptic signals by examining perceptual thresholds in three different scenarios using (i) the dominant hand, (ii) the non-dominant hand, and (iii) both hands simultaneously to differentiate between two successive signals. Subjects exposed to force signals in these three situations conveyed their perceptions of alterations in signal magnitude after each trial. Subsequently, we applied psychometric functions to the collected responses to determine perceptual thresholds. Our results indicate a substantial difference in threshold values between bi-manual and uni-manual scenarios, with the bi-manual scenario exhibiting higher thresholds, indicating inferior perceptual ability when both hands are simultaneously utilized in two separate discrimination tasks. Furthermore, our investigation reveals distinct perception thresholds between the dominant and non-dominant hands, owing to differences in the perceptual capability of the two hands. These findings provide substantial insight into how the nature of tasks may alter kinesthetic perception, offering implications for the development of haptic interfaces in practical applications.

Sensory Schwann cells set perceptual thresholds for touch and selectively regulate mechanical nociception.

Previous work identified nociceptive Schwann cells that can initiate pain. Consistent with the existence of inherently mechanosensitive sensory Schwann cells, we found that in mice, the mechanosensory function of almost all nociceptors, including those signaling fast pain, were dependent on sensory Schwann cells. In polymodal nociceptors, sensory Schwann cells signal mechanical, but not cold or heat pain. Terminal Schwann cells also surround mechanoreceptor nerve-endings within the Meissner's corpuscle and in hair follicle lanceolate endings that both signal vibrotactile touch. Within Meissner´s corpuscles, two molecularly and functionally distinct sensory Schwann cells positive for Sox10 and Sox2 differentially modulate rapidly adapting mechanoreceptor function. Using optogenetics we show that Meissner's corpuscle Schwann cells are necessary for the perception of low threshold vibrotactile stimuli. These results show that sensory Schwann cells within diverse glio-neural mechanosensory end-organs are sensors for mechanical pain as well as necessary for touch perception.

Odor dilution sorting as a clinical test of olfactory function: normative values and reliability data.

Clinical assessment of an individual's sense of smell has gained prominence, but its resource-intensive nature necessitates the exploration of self-administered methods. In this study, a cohort of 68 patients with olfactory loss and 55 controls were assessed using a recently introduced olfactory test. This test involves sorting 2 odorants (eugenol and phenylethyl alcohol) in 5 dilutions according to odor intensity, with an average application time of 3.5 min. The sorting task score, calculated as the mean of Kendall's Tau between the assigned and true dilution orders and normalized to [0,1], identified a cutoff for anosmia at a score ≤ 0.7. This cutoff, which marks the 90th percentile of scores obtained with randomly ordered dilutions, had a balanced accuracy of 89% (78% to 97%) for detecting anosmia, comparable to traditional odor threshold assessments. Retest evaluations suggested a score difference of ±0.15 as a cutoff for clinically significant changes in olfactory function. In conclusion, the olfactory sorting test represents a simple, self-administered approach to the detection of anosmia or preserved olfactory function. With balanced accuracy similar to existing brief olfactory tests, this method offers a practical and user-friendly alternative for screening anosmia, addressing the need for resource-efficient assessments in clinical settings.

Changes in sensitivity and hedonic rating to transcutaneous electrical nerve stimulation following COVID-19.

COVID-19 affects not only the respiratory system but also other biological systems such as the nervous system. Usually, these changes are reported based on the patient's subjective description. The aim of our study, therefore, was to objectively determine the effect that the SARS-CoV-2 virus and COVID-19 disease has on sensory threshold and the hedonic and subjective perception of an electrical stimulus. The sensory threshold was tested on the inner forearm by applying non-invasive transcutaneous electrical nerve stimulation (TENS) with 100 Hz and 100 µs parameters and a biphasic current waveform. The study involved 211 participants, aged 22-79 years, with a mean age of 56.9 ± 12.1 years. There were 131 subjects in the COVID group, while the NON-COVID group, the control group, was matched to the COVID group in terms of gender, age, body mass index and presence of chronic diseases. The research was carried out in 2022. Sensory sensitivity was highest in the group that had suffered with COVID-19. The median sensory sensitivity was 11 mA in the COVID group and 14 mA (p < 0.001) in the NON-COVID group, however, the current sensitivity threshold decreased over time (R = 0.52, p < 0.001). Post COVID-19, the electrical stimulus was more often perceived as unpleasant: COVID versus NON-COVID (23% vs. 3%, p < 0.001) and as a different sensation to tingling (27% vs. 2%, p < 0.001). Post-COVID-19 patients have a lower sensory threshold, the electrical stimulus is more often described as unpleasant and in subjective feelings it is more often described as pinching. The differences between COVID and NON-COVID decrease with time since the onset of COVID symptoms.

The "Sniffin' Kids-PT" test: A smell test variant for Portuguese children.

OBJECTIVE: Olfactory tests tailored for children are essential, as diagnosing olfactory dysfunction at these ages can be challenging. The 16-item "Sniffin' Sticks" is reliable and easy to perform. To the best of our knowledge, there is currently no validated olfactory test for the Portuguese pediatric population. This study aimed to adapt and validate the "Sniffin' Sticks" olfactory test for the Portuguese pediatric population. METHODS: Between August 2020 and September 2021, 354 children aged between 6 and 17years old enrolled in the study, 336 healthy children with a normal sense of smell, and 18 anosmic children with Kallmann syndrome. The study consisted of two parts. Firstly, the "Sniffin' Sticks" olfactory identification test was applied to healthy children and the odors with statistically significant low identification rates were excluded. A modified version of "Sniffin' Sticks" was defined and named "Sniffin' Kids-PT" test. Secondly, normative data were assessed and test-retest and validation tests were performed. RESULTS: Apple and Cloves odors were identified with a low rate and were excluded from the "Sniffin' Sticks" olfactory test. In the modified 14-item "Sniffin' Kids-PT", scoring <6 (from 6-8years old), <7 (from 9-11years old) or <8 (from 12-14years old and 15-17years old) was indicative of olfactory dysfunction. The test-retest reliability was good (r=0.81; P<0.001) and the differences between scores of healthy children and anosmic children were statistically significant (U213=13.00; P<0.001). CONCLUSION: The modified "Sniffin' Kids-PT" is a reliable test to discriminate between normosmia and olfactory dysfunction in Portuguese children over 5years old.

Quantitative sensory testing defines the trajectory of sensory neuropathy after severe COVID-19.

AIMS: To assess sensory neuropathy development after severe COVID-19. METHODS: Patients with severe COVID-19 underwent assessment of neuropathic symptoms, tendon reflexes, and quantitative sensory testing to evaluate vibration (VPT), cold (CPT), warm (WPT) and heat perception thresholds (HPT) within 1-3 weeks of admission and after 1-year. RESULTS: 32 participants with severe COVID-19 aged 68.6 ± 12.4 (18.8 % diabetes) were assessed. At baseline, numbness and neuropathic pain were present in 56.3 % and 43.8 % of participants, respectively. On the feet, VPT, WPT, and HPT were abnormal in 81.3 %, CPT was abnormal in 50.0 % and HPT on the face was abnormal in 12.5 % of patients. At 1-year follow-up, the prevalence of abnormal VPT (81.3 % vs 50.0 %, P < 0.01), WPT (81.3 % vs 43.8 %, P < 0.01), and HPT (81.3 % vs 50.0 %, P < 0.01) decreased, with no change in CPT (P = 0.21) on the feet or HPT on the face (P = 1.0). Only participants without diabetes recovered from an abnormal VPT, CPT, and WPT. Patients with long-COVID (37.5 %) had comparable baseline VPT, WPT and CPT with those without long-COVID (P = 0.07-0.69). CONCLUSIONS: Severe COVID-19 is associated with abnormal vibration and thermal thresholds which are sustained for up to 1 year in patients with diabetes. Abnormal sensory thresholds have no association with long-COVID development.

Intranasal insulin for COVID-19-related smell loss.

BACKGROUND: Quantitative (hyposmia and anosmia) and qualitative (phantosmia and parosmia) olfactory disorders are common consequences of COVID-19 infection found in more than 38% of patients even months after resolution of acute disease. SARS-CoV-2 has tropism for angiotensin-converting enzyme 2 (ACE2) in the respiratory system, suggesting that it is the mechanism of damage to the olfactory neuroepithelium and of involvement at the central nervous system. The olfactory bulb is the organ with the highest insulin uptake in the central nervous system. Insulin increases the production of Growth Factors (GF); therefore, in this study, the administration of intranasal insulin is proposed as a viable treatment for olfactory disturbances. The aim of this study was to obtain improvement in olfaction after 4 weeks of intranasal insulin administration in a group of patients presenting chronic olfactory disturbances secondary to COVID-19 infection, quantified using the Threshold, Discrimination, and Identification (TDI) score based on the Sniffin Sticks®. METHODS: Experimental, longitudinal, prolective and prospective study of patients with a previous diagnosis of COVID-19 in the last 3-18 months and who persisted with anosmia or hyposmia. The sample size was calculated with "satulator". The intervention was performed from January to May 2022. Throughout four appointments, a baseline olfactory measurement was obtained using the TDI score based on the Sniffin Sticks® test. In the first three appointments, Gelfoam® cottonoids soaked in 40 IU of NPH insulin were placed on the nasal roof of each nostril for 15 min. Descriptive statistics, student's paired t test and a multiple linear regression were utilized to ascertain statistical significance of the outcome on the TDI score obtained on the fourth and final appointment. RESULTS: 27 patients were included in the study. Table 1 summarizes the sample characteristics. The results exhibit that 93% of the sample had an improvement. The initial mean TDI score was 67% (63-71) compared to the final mean of 83% (80-86, p < 0.01). TDI subsection analysis is shown in Table 2. There was no significant difference in pre-intervention and post-intervention glucose measurements after the intranasal insulin administration. CONCLUSIONS: The administration of intranasal insulin has promising results, pointing towards an alternative of treatment for chronic olfactory disturbances secondary to neuroepithelial damage caused by upper respiratory tract infections. Furthermore, this is the first study to use a three-point assessment of olfaction in post-COVID-19 patients, while using the Sniffin Sticks® TDI score adapted to Latin Spanish.

Underestimated olfactory domains in Huntington's disease: odour discrimination and threshold.

BACKGROUND: Olfaction has recently found clinical value in prediction, discrimination and prognosis of some neurodegenerative disorders. However, data originating from standard tests on olfactory dysfunction in Huntington's disease are limited to odour identification, which is only one domain of olfactory perceptual space. METHOD: Twenty-five patients and 25 age- and gender-matched controls were evaluated by the Sniffin' Sticks test in three domains of odour threshold, odour discrimination, odour identification and the sum score of them. Patients' motor function was assessed based on the Unified Huntington's Disease Rating Scale. RESULTS: Compared with controls, patients' scores of all olfactory domains and their sum were significantly lower. Besides, our patients' odour threshold and odour discrimination impairments were more frequently impaired than odour identification impairment (86 per cent and 81 per cent vs 34 per cent, respectively). CONCLUSION: Olfactory impairment is a common finding in patients with Huntington's disease; it is not limited to odour identification but is more pronounced in odour discrimination and odour threshold.

Examining Increment thresholds as a function of pedestal contrast under hypothetical parvo- and magnocellular-biased conditions.

Theoretically, the pulsed- and steady-pedestal paradigms are thought to track contrast-increment thresholds (ΔC) as a function of pedestal contrast (C) for the parvocellular (P) and magnocellular (M) systems, respectively, yielding linear ΔC versus C functions for the pulsed- and nonlinear functions for the steady-pedestal paradigm. A recent study utilizing these paradigms to isolate the P and M systems reported no evidence of the M system being suppressed by red light, contrary to previous physiological and psychophysical findings. Curious as to why this may have occurred, we examined how ΔC varies with C for the P and M systems using the pulsed- and steady-pedestal paradigms and stimuli biased towards the P or M systems based on their sensitivity to spatial frequency (SF) and color. We found no effect of color and little influence of SF. To explain this lack of color effects, we used a quantitative model of ΔC (as it changes with C) to obtain Csat and contrast-gain values. The contrast-gain values (i) contradicted the hypothesis that the steady-pedestal paradigm tracks the M-system response, and (ii) our obtained Csat values indicated strongly that both pulsed- and steady-pedestal paradigms track primarily the P-system response.

Monocular and binocular mechanisms detect modulations of dot density and dot contrast.

Strong reciprocity has been demonstrated between (1) spatial modulations of dot density and modulations of dot luminance, and (2) modulations of dot density and modulations of dot contrast, in textures. The latter are much easier to detect when presented in phase with one another than when presented 180° out of phase, although out-of-phase modulations can also be detected given sufficient amplitude. This result supports the existence of two detection mechanisms: one that is excited by both density modulations and contrast modulations (quiescent when those modulations are presented 180° out of phase) and another that is relatively insensitive to either density modulations or contrast modulations (thus remaining stimulated regardless of phase angle). We investigate whether the mechanism responsible for detecting out-of-phase modulations depends on high-level computations (downstream from the confluence of monocular signals) or whether both mechanisms are situated at the monocular level of visual processing. Specifically, density-modulated and/or contrast-modulated stimuli were presented monocularly (i.e., to the same eye) or dichoptically (i.e., to opposite eyes). Out-of-phase modulations of density were much easier to detect when presented dichoptically. A dichoptic advantage was also found for out-of-phase density and contrast modulations. These dichoptic advantages imply conscious access to a mechanism at the monocular level of processing. When density modulations were presented dichoptically, 180° out of phase, detection thresholds were highest. Consequently, a mechanism with binocular input must also contribute to the detection of these modulations. We describe a minimal, image-based model for these results that contains one monocular computation and one binocular computation.

Human vestibular perceptual thresholds - A systematic review of passive motion perception.

BACKGROUND: The vestibular system detects head accelerations within 6 degrees of freedom. How well this is accomplished is described by vestibular perceptual thresholds. They are a measure of perceptual performance based on the conscious evaluation of sensory information. This review provides an integrative synthesis of the vestibular perceptual thresholds reported in the literature. The focus lies on the estimation of thresholds in healthy participants, used devices and stimulus profiles. The dependence of these thresholds on the participants clinical status and age is also reviewed. Furthermore, thresholds from primate studies are discussed. RESULTS: Thresholds have been measured for frequencies ranging from 0.05 to 5 Hz. They decrease with increasing frequency for five of the six main degrees of freedom (inter-aural, head-vertical, naso-occipital, yaw, pitch). No consistent pattern is evident for roll rotations. For a frequency range beyond 5 Hz, a U-shaped relationship is suggested by a qualitative comparison to primate data. Where enough data is available, increasing thresholds with age and higher thresholds in patients compared to healthy controls can be observed. No effects related to gender or handedness are reported. SIGNIFICANCE: Vestibular thresholds are essential for next generation screening tools in the clinical domain, for the assessment of athletic performance, and workplace safety alike. Knowledge about vestibular perceptual thresholds contributes to basic and applied research in fields such as perception, cognition, learning, and healthy aging. This review provides normative values for vestibular thresholds. Gaps in current knowledge are highlighted and attention is drawn to specific issues for improving the inter-study comparability in the future.