Hyper-Arousal Decreases Human Visual Thresholds

Arousal has long been known to influence behavior and serves as an underlying component of cognition and consciousness. However, the consequences of hyper-arousal for visual perception remain unclear. The present study evaluates the impact of hyper-arousal on two aspects of visual sensitivity: visual stereoacuity and contrast thresholds. Sixty-eight participants participated in two experiments. Thirty-four participants were randomly divided into two groups in each experiment: Arousal Stimulation or Sham Control. The Arousal Stimulation group underwent a 50-second cold pressor stimulation (immersing the foot in 0–2° C water), a technique known to increase arousal. In contrast, the Sham Control group immersed their foot in room temperature water. Stereoacuity thresholds (Experiment 1) and contrast thresholds (Experiment 2) were measured before and after stimulation. The Arousal Stimulation groups demonstrated significantly lower stereoacuity and contrast thresholds following cold pressor stimulation, whereas the Sham Control groups showed no difference in thresholds. These results provide the first evidence that hyper-arousal from sensory stimulation can lower visual thresholds. Hyper-arousal''s ability to decrease visual thresholds has important implications for survival, sports, and everyday life.     

The role of stimulus structure in spatial hyperacuity

In spatial hyperacuity the subjects discriminate a stimulus feature relative to a reference, with an accuracy significantly better than the grain of the retinal mosaic. We show that the normalized thresholds have a dichotomous behavior; they are either insensitive to the spatial parameter in the experiment or increase very steeply with it. This behavior is explained by the involvement in the processing of pixel (receptor) accuracy information about the structure of the stimulus. A computational model employing optimal filtering reproduces the experimental data and suggests that processing of spatial hyperacuity tasks in the human visual system is optimal.     

Differential spatial displacement discrimination with interfering stimuli

Differential spatial displacement discrimination thresholds were determined for a configuration of three blobs with Gaussian spatial and temporal contrast envelopes. This task is similar to the well known three-dot alignment hyperacuity task. Thresholds determined in the presence of interfering stimuli were identical to thresholds determined without these flanking stimuli. The thresholds scale linearly with stimulus size over at least two decades. We conclude that (i) the mechanisms that compute differential spatial displacement for the three-blob alignment task are not disturbed by the presence of neighbouring stimuli, even when these enter the region over which the computations are performed and (ii) at all levels of resolution similar mechanisms are used to compute differential spatial displacement.     

A simple model of human foveal ganglion cell responses to hyperacuity stimuli

We developed a physiologically plausible model of the first steps of spatial visual information processing in the fovea of the human retina. With the predictions of this model we could support the hypothesis that, for moderate contrasts ( 40%), hyperacuity is mediated by the magnocellular (MC-) pathway. Despite the lower sampling density in the MC pathway, as compared to the parvocellular (PC-) pathway, the information that is transferred by the MC ganglion cells is sufficient to achieve thresholds comparable to those of human subjects in psychophysical tasks. This is a result of the much higher signal-to-noise ratio of the MC pathway cell signals. The PC pathway cells do not transfer enough information for hyperacuity thresholds.     

Visual acuity and hyperacuity in 11- to 17-year-old secondary school students

Visual acuity and hyperacuity of 11- to 17-year-old secondary school students with normal vision were measured and compared. The estimations of hyperacuity and acuity were made using the vernier stimuli, Landolt Cs, and Tumbling Es. When test stimuli were located in the tables, visual acuity estimations measured using Landolt Cs were significantly higher by a factor of 1.1 than that measured using Tumbling Es. Visual hyperacuity was 1.25?C4.1 times higher than visual acuity. The estimations of visual hyperacuity were almost 2 times higher in 16-year-old than 13-year-old secondary school students, in contrast to the estimations of visual acuity that did not change with age. The binocular visual acuity estimations were 1.05 times higher than the monocular ones and did not depend on the age. The ratio of binocular visual hyperacuity to monocular visual hyperacuity in 13-year-old secondary school students was 1.9, whereas, in senior secondary school students, it was 1.2. The contribution of binocular vision to the development of the mechanisms of visual acuity and hyperacuity in ontogenesis and the differences between the mechanisms of visual acuity and hyperacuity are discussed.     

Discrimination thresholds for channel-coded systems

We present an analytical ideal observer model to predict discrimination thresholds for stimuli that are processed by arrays of noise-perturbed receptors that have smooth and overlapping tuning functions. We show that hyperacuity phenomena are natural properties of these systems. A comparison of thresholds for a number of discrimination tasks allows a psychophysically derived estimate of parameters of the receptor array involved. We note the consistency of this scheme with data from a number of visual subfields.     

人的体视超视锐度阈值

体视超视(?)象是视觉系统中(?)度的超(?)在一些特殊的(?)图形下,它的阈值可达2秒以下.考虑到人眼的一般体(?)锐度的60(?),(?)未超视度现象就是一个很有意义并值得注意研究的问题.对于如此精细的分辨能力,视(?)膜细胞可以说是很粗糙的(其直径约24秒)我们想了解,这么粗糙的视网膜是如何分辨出仅为其直径1/10的目标位差的呢?本文对人眼体视超视锐度现象做了一此研究,测定出体视超视锐度(?)值,并研究了低通滤波后对其影响.     

The detection of spatial discontinuities: interactions between contrast and spatial contiguity

Thresholds were measured for the detection of spatial discontinuities (notches and bumps) along luminance boundaries. At high contrasts of the boundary, thresholds expressed in terms of the spatial notch/bump height fell well inside the hyperacuity range. Expressed as luminance increment thresholds between adjacent photoreceptors, the same thresholds were similar to those previously reported by Hartridge and by Hecht and Mintz for the detection of a single line. The ability of observers to detect differences in the height of a boundary on either side of a mean luminance gap was also investigated, and the effect of the gap was found to depend upon stimulus contrast. At high contrasts the introduction of a gap increased thresholds, but at the lowest contrasts, thresholds were unaffected by a gap. The role of different spatial frequency and orientational mechanisms in vernier acuity is discussed.     

Orientation Transfer in Vernier and Stereoacuity Training

Human performance on various visual tasks can be improved substantially via training. However, the enhancements are frequently specific to relatively low-level stimulus dimensions. While such specificity has often been thought to be indicative of a low-level neural locus of learning, recent research suggests that these same effects can be accounted for by changes in higher-level areas–in particular in the way higher-level areas read out information from lower-level areas in the service of highly practiced decisions. Here we contrast the degree of orientation transfer seen after training on two different tasks—vernier acuity and stereoacuity. Importantly, while the decision rule that could improve vernier acuity (i.e. a discriminant in the image plane) would not be transferable across orientations, the simplest rule that could be learned to solve the stereoacuity task (i.e. a discriminant in the depth plane) would be insensitive to changes in orientation. Thus, given a read-out hypothesis, more substantial transfer would be expected as a result of stereoacuity than vernier acuity training. To test this prediction, participants were trained (7500 total trials) on either a stereoacuity (N = 9) or vernier acuity (N = 7) task with the stimuli in either a vertical or horizontal configuration (balanced across participants). Following training, transfer to the untrained orientation was assessed. As predicted, evidence for relatively orientation specific learning was observed in vernier trained participants, while no evidence of specificity was observed in stereo trained participants. These results build upon the emerging view that perceptual learning (even very specific learning effects) may reflect changes in inferences made by high-level areas, rather than necessarily fully reflecting changes in the receptive field properties of low-level areas.     

人类视觉系统超视锐度现象的神经网络数学模型研究

超视锐度是人们熟知的奇特现象,虽然许多视觉研究领域中的专家们对此做了大量的研究,但视觉系统究竟是如何提取超视锐度信息的却仍然是个未解决的问题.本文用简单细胞广义Gabor函数为基本功能单元,以Marr提出的计算理论为框架,建立了一个感受野重叠的,具有比较运算性质的、可解释超视锐度现象的神经网络数学模型.它在空间比较,真实运动和似动三方面较好地描述了已有的一些有关超视锐度现象的心理物理实验结果.     

Acuity and hyperacuity for pupils of 11-17 years old

Estimations of hyperacuity and visual acuity (VA) have been compared in schoolchildren aged 11-17 years with normal vision. VA was measured using Landolt Cs and Tumbling Es. Hyperacuity was measured by vernier stimuli. Acuity estimations depended on the test stimuli. They were in 1.1 times over for Landolt Cs than for Tumbling Es. Hyperacuity estimations exceeded VA in 1.25-4.1 times. They were almost twice as high among pupils of 16 years compared to 13-year-olds, in contrast to estimates of VA, which practically did not change with age. Binocular VA was significantly higher monocular VA in 1.05 times regardless of age. The ratio between the binocular and monocular hyperacuity estimates for thirteen years pupils in average was equal to 1.9, while for sixteen years pupils--1.2. We discuss the contribution of binocular vision in the development of mechanisms of VA and hyperacuity in ontogenesis and the difference between these mechanisms.     

Experiment Research on Binocular Perceptual Characteristics around Peripheral Vision for Development of Head Mounted Display with Wide View

The head mounted display （HMD） is widely used in virtual reality technology. In common HMD, however, the binocular disparity is set to an equal fixed value in the entire range of view. Such HMD systems have several shortcomings when used for wide views. In this study, in order to realize a natural stereo sensation of HMD with wide view, we measure the characteristics of binocular stereo perception and binocular light perception. Results show that both the stereoacuity and light sensitivity decrease as the retina＇s eccentricity increases from fovea to periphery. However, the decrease of the stereoacuity is more rapid than that of the light sensitivity. These results suggest that the binocular disparity at the peripheral field should be small, otherwise double images would be observed instead of a stereo view. Based on the results we develop a relative binocular stereoacuity model which can be applied for the design of HMD systems with wide view.     

生态阈值研究进展

生态阈值是指生态系统从一种状态快速转变为另一种状态的某个点或一段区间,推动这种转变的动力来自某个或多个关键生态因子微弱的附加改变。生态阈值现象普遍存在于自然生态系统中。主要有两种类型：生态阈值点（ecological threshold point）和生态阈值带（ecological threshold zone）。在生态阈值点前后,生态系统的特性、功能或过程发生迅速的改变。生态阈值带暗含了生态系统从一种稳定状态到另一稳定状态逐渐转换的过程,而不像点型阈值那样发生突然的转变。后者在自然界中可能更为普遍。在自然资源保护和生态系统可持续管理中,生态阈值研究有着重要的理论和实践意义,受到生态学和相关学科的密切关注。其研究已经在森林、草原、湖泊、海洋等生态系统,从不同角度,针对不同生态因子广泛开展。由于生态因子相互作用的复杂性,有关生态阈值的性质及其在不同空间尺度上的联系仍然存在很大的不确定性。在未来的研究中必须加强综合和定量化研究,进一步提高应用生态阈值的能力。在全球变化和生态响应研究领域,生态阈值研究将会有更大的发展空间。     

Stereoacuity with Frisby and Revised FD2 Stereo Tests

We compared near stereoacuity, measured with the Frisby test, and distance stereoacuity, measured with the revised Frisby-Davis (FD2) test, enabling a comparison with the original version of the FD2. In the revised version of the FD2 test, a white background is used instead of a backlit background. We also examined the effect of age, gender and visual problems. We used the Frisby test at distances ranging from 30–80 cm and FD2 at 6 m. The best possible score was 20 seconds of arc (arcsec) on the Frisby and 5 arcsec on the FD2; participants who could not perform a test despite demonstrating understanding of it were classed as stereonegative. We examined both the whole population recruited, and a sub-population screened so as to exclude visual problems. We analysed our results in three age-groups: “visually developing” (36 children aged 5–10 years); “visually mature” (300 participants aged 11–49 years) and “older” (29 participants aged 50–82). In the whole population, the median stereoacuity on the Frisby test was 25, 20 and 85 arcsec in the three age-groups. In the sub-population with no visual problems, median Frisby stereoacuity was similar at 20, 20 and 80 arcsec respectively. On the FD2, the medians were 10, 10, 20 arcsec for the whole population and 7.5, 10 and 12.5 for the sub-population. Children were more likely than adults to be stereonegative on the FD2, although none of the children were stereonegative on the Frisby. The two tests showed fair agreement when used to classify people into three categories of stereovision. Poor stereovision was often associated with binocular problems such as tropia, but with many exceptions. In line with previous studies, we found improvements in measured stereoacuity in childhood and declines in late adulthood. The new FD2 test gives comparable values to the original FD2.     

Vibrotactile difference thresholds: Effects of vibration frequency,vibration magnitude,contact area,and body location

It has not been established whether the smallest perceptible change in the intensity of vibrotactile stimuli depends on the somatosensory channel mediating the sensation. This study investigated intensity difference thresholds for vibration using contact conditions (different frequencies, magnitudes, contact areas, body locations) selected so that perception would be mediated by more than one psychophysical channel. It was hypothesized that difference thresholds mediated by the non-Pacinian I (NPI) channel and the Pacinian (P) channel would differ. Using two different contactors (1-mm diameter contactor with 1-mm gap to a fixed surround; 10-mm diameter contactor with 2-mm gap to the surround) vibration was applied to the thenar eminence and the volar forearm at two frequencies (10 and 125?Hz). The up-down-transformed-response method with a three-down-one-up rule provided absolute thresholds and also difference thresholds at various levels above the absolute thresholds of 12 subjects (i.e., sensation levels, SLs) selected to activate preferentially either single channels or multiple channels. Median difference thresholds varied from 0.20 (thenar eminence with 125-Hz vibration at 10?dB SL) to 0.58 (thenar eminence with 10-Hz vibration at 20?dB SL). Median difference thresholds tended to be lower for the P channel than the NPI channel. The NPII channel may have reduced difference thresholds with the smaller contactor at 125?Hz. It is concluded that there are large and systematic variations in difference thresholds associated with the frequency, the magnitude, the area of contact, and the location of contact with vibrotactile stimuli that cannot be explained without increased understanding of the perception of supra-threshold vibrotactile stimuli.     

Minimum area thresholds for rattlesnakes and colubrid snakes on islands in the Gulf of California,Mexico

We expand a framework for estimating minimum area thresholds to elaborate biogeographic patterns between two groups of snakes (rattlesnakes and colubrid snakes) on islands in the western Gulf of California, Mexico. The minimum area thresholds for supporting single species versus coexistence of two or more species relate to hypotheses of the relative importance of energetic efficiency and competitive interactions within groups, respectively. We used ordinal logistic regression probability functions to estimate minimum area thresholds after evaluating the influence of island area, isolation, and age on rattlesnake and colubrid occupancy patterns across 83 islands. Minimum area thresholds for islands supporting one species were nearly identical for rattlesnakes and colubrids (~1.7 km²), suggesting that selective tradeoffs for distinctive life history traits between rattlesnakes and colubrids did not result in any clear advantage of one life history strategy over the other on islands. However, the minimum area threshold for supporting two or more species of rattlesnakes (37.1 km²) was over five times greater than it was for supporting two or more species of colubrids (6.7 km²). The great differences between rattlesnakes and colubrids in minimum area required to support more than one species imply that for islands in the Gulf of California relative extinction risks are higher for coexistence of multiple species of rattlesnakes and that competition within and between species of rattlesnakes is likely much more intense than it is within and between species of colubrids.     

Comparison of auditory functions in the chimpanzee and human

Absolute thresholds for pure tones, loudness, frequency and intensity difference thresholds and the resonance of the external auditory meatus were measured in chimpanzees and compared with those in humans. Chimpanzees were more sensitive than humans to frequencies higher than 8 kHz but less sensitive to frequencies lower than 250 Hz and 2- to 4-kHz tones. Difference thresholds for frequency and intensity were greater in chimpanzees than in humans. The resonance of the external ear was about the same in the two species. The effects of differences in hearing between species upon speech perception are discussed.     

Laterality and sex differences in tactile detection and two-point thresholds modified by body surface area and body fat ratio

Tactile detection and two-point discrimination tests are commonly used in neurological examinations. However, questions remain about the influence of both body and patient characteristics on test thresholds. The left side of the body has sometimes been reported more tactilely sensitive than the right, and females are said to be more sensitive than males. We measured tactile detection and two-point discrimination thresholds on the finger, palm, and forehead of a large sample of young adults (N=171), examining laterality and sex differences, and the effects of body surface area (BSA) and body fat ratio (BFR). In tactile detection, there were no effects of laterality, BSA, or BFR, although females had lower thresholds than males. In two-point discrimination, there was an effect of laterality, with lower thresholds on the left side. This probably reflects hemispheric spatial processing differences. A significant BFR effect implies that subcutaneous fat affects skin deformation, but there were no effects of sex or BSA. The two-point discrimination findings differ in several respects from recent findings using grating orientation discriminations. A small positive correlation between the tasks, falling far short of test-retest reliabilities, indicates that they use largely disjoint but partially overlapping processes.     

Integration of Semi-Circular Canal and Otolith Cues for Direction Discrimination during Eccentric Rotations

Humans are capable of moving about the world in complex ways. Every time we move, our self-motion must be detected and interpreted by the central nervous system in order to make appropriate sequential movements and informed decisions. The vestibular labyrinth consists of two unique sensory organs the semi-circular canals and the otoliths that are specialized to detect rotation and translation of the head, respectively. While thresholds for pure rotational and translational self-motion are well understood surprisingly little research has investigated the relative role of each organ on thresholds for more complex motion. Eccentric (off-center) rotations during which the participant faces away from the center of rotation stimulate both organs and are thus well suited for investigating integration of rotational and translational sensory information. Ten participants completed a psychophysical direction discrimination task for pure head-centered rotations, translations and eccentric rotations with 5 different radii. Discrimination thresholds for eccentric rotations reduced with increasing radii, indicating that additional tangential accelerations (which increase with radius length) increased sensitivity. Two competing models were used to predict the eccentric thresholds based on the pure rotation and translation thresholds: one assuming that information from the two organs is integrated in an optimal fashion and another assuming that motion discrimination is solved solely by relying on the sensor which is most strongly stimulated. Our findings clearly show that information from the two organs is integrated. However the measured thresholds for 3 of the 5 eccentric rotations are even more sensitive than predictions from the optimal integration model suggesting additional non-vestibular sources of information may be involved.     

New Stereoacuity Test Using a 3-Dimensional Display System in Children

The previously developed 3-dimensional (3D) display stereoacuity tests were validated only at distance. We developed a new stereoacuity test using a 3D display that works both at near and distance and evaluated its validity in children with and without strabismus. Sixty children (age range, 6 to 18 years) with variable ranges of stereoacuity were included. Side-by-side randot images of 4 different simple objects (star, circle, rectangle, and triangle) with a wide range of crossed horizontal disparities (3000 to 20 arcsec) were randomly displayed on a 3D monitor with MATLAB (Matworks, Inc., Natick, MA, USA) and were presented to subjects wearing shutter glasses at 0.5 m and 3 m. The 3D image was located in front of (conventional) or behind (proposed) the background image on the 3D monitor. The results with the new 3D stereotest (conventional and proposed) were compared with those of the near and distance Randot stereotests. At near, the Bland-Altman plots of the conventional and proposed 3D stereotest did not show significant difference, both of which were poorer than the Randot test. At distance, the results of the proposed 3D stereotest were similar to the Randot test, but the conventional 3D stereotest results were better than those of the other two tests. The results of the proposed 3D stereotest and Randot stereotest were identical in 83.3% at near and 88.3% at distance. More than 95% of subjects showed concordance within 2 grades between the 2 tests at both near and distance. In conclusion, the newly proposed 3D stereotest shows good concordance with the Randot stereotests in children with and without strabismus.