Spatial and Temporal Abnormalities of Spontaneous Fixational Saccades and Their Correlates With Positive and Cognitive Symptoms in Schizophrenia.

BACKGROUND AND HYPOTHESIS: Visual fixation is a dynamic process, with the spontaneous occurrence of microsaccades and macrosaccades. These fixational saccades are sensitive to the structural and functional alterations of the cortical-subcortical-cerebellar circuit. Given that dysfunctional cortical-subcortical-cerebellar circuit contributes to cognitive and behavioral impairments in schizophrenia, we hypothesized that patients with schizophrenia would exhibit abnormal fixational saccades and these abnormalities would be associated with the clinical manifestations. STUDY DESIGN: Saccades were recorded from 140 drug-naïve patients with first-episode schizophrenia and 160 age-matched healthy controls during ten separate trials of 6-second steady fixations. Positive and negative symptoms were assessed using the Positive and Negative Syndrome Scale (PANSS). Cognition was assessed using the Measurement and Treatment Research to Improve Cognition in Schizophrenia Consensus Cognitive Battery (MCCB). STUDY RESULTS: Patients with schizophrenia exhibited fixational saccades more vertically than controls, which was reflected in more vertical saccades with angles around 90° and a greater vertical shift of horizontal saccades with angles around 0° in patients. The fixational saccades, especially horizontal saccades, showed longer durations, faster peak velocities, and larger amplitudes in patients. Furthermore, the greater vertical shift of horizontal saccades was associated with higher PANSS total and positive symptom scores in patients, and the longer duration of horizontal saccades was associated with lower MCCB neurocognitive composite, attention/vigilance, and speed of processing scores. Finally, based solely on these fixational eye movements, a K-nearest neighbors model classified patients with an accuracy of 85%. Conclusions: Our results reveal spatial and temporal abnormalities of fixational saccades and suggest fixational saccades as a promising biomarker for cognitive and positive symptoms and for diagnosis of schizophrenia.

Gestalt neurons and emergent properties in visual perception: A novel concept for the transformation from local to global processing.

Gestalten in visual perception are defined by emergent properties of the whole, which cannot be predicted from the sum of its parts; rather, they arise by virtue of inherent principles, the Laws of Seeing. This review attempts to assign neurophysiological correlates to select emergent properties in motion and contour perception and proposes parallels to the processing of local versus global attributes by classical versus contextual receptive fields. The aim is to identify Gestalt neurons in the visual system to account for the Laws of Seeing in causal terms and to explain "Why do things look as they do" (Koffka, 1935, p. 76).

Glimpses from the past: Michael Wertheimer dead at 95.

Michael was a historian by choice and calling, well-known for his Brief History of Psychology, which appeared in six editions. He also edited with Gregory Kimble a seven-volume series of Portraits of Pioneers in Psychology, an essential resource describing many of the illustrious ancestors of contemporary psychology. He was known for his long service to various professional associations, especially the APA. He was president of four APA divisions: 1 (General Psychology), 2 (Teaching of Psychology), 24 (Theoretical and Philosophical Psychology), and 26 (History of Psychology). These commitments show his extraordinary social conscience. In the Psychology Department at CU Boulder, he was highly respected for his superior knowledge and quick curiosity, but also feared for his critical questions and comments. Michael was not one to socialize with and enjoy small talk the way most of us do. Rather, his conversations were brief, to the point, and strictly academic. However, the author also learnt that behind his formal and reserved outward appearance, there was a charming, humorous, and cheerful Mensch. But most of all he was a scholar of universal knowledge, rare passion, and exemplary devotion. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Heinrich Müller (1820-1864) and the entoptic discovery of the site in the retina where vision is initiated.

Heinrich Müller was a nineteenth-century German retinal anatomist who, during his short career, was one of the discoverers of the rod photopigment rhodopsin and neuroglia in the retina, now known as Müller cells. He also described the ocular muscles and double foveae of some birds. An important, but largely neglected, insight by Müller was to combine careful psychophysical measurements and geometrical optics to find the location of the photosensitive layer of the retina in the living eye. Here, we provide translated passages from Müller's (1855) publication and compare his entoptic observations with retinal imaging using optical coherence tomography. Müller correctly deduced from his careful experiments that vision is initiated in the photoreceptors located in the back of the retina.

Body Pitch Together With Translational Body Motion Biases the Subjective Haptic Vertical.

Accurate perception of verticality is critical for postural maintenance and successful physical interaction with the world. Although previous research has examined the independent influences of body orientation and self-motion under well-controlled laboratory conditions, these factors are constantly changing and interacting in the real world. In this study, we examine the subjective haptic vertical in a real-world scenario. Here, we report a bias of verticality perception in a field experiment on the Hong Kong Peak Tram as participants traveled on a slope ranging from 6° to 26°. Mean subjective haptic vertical (SHV) increased with slope by as much as 15°, regardless of whether the eyes were open (Experiment 1) or closed (Experiment 2). Shifting the body pitch by a fixed degree in an effort to compensate for the mountain slope failed to reduce the verticality bias (Experiment 3). These manipulations separately rule out visual and vestibular inputs about absolute body pitch as contributors to our observed bias. Observations collected on a tram traveling on level ground (Experiment 4A) or in a static dental chair with a range of inclinations similar to those encountered on the mountain tram (Experiment 4B) showed no significant deviation of the subjective vertical from gravity. We conclude that the SHV error is due to a combination of large, dynamic body pitch and translational motion. These observations made in a real-world scenario represent an incentive to neuroscientists and aviation experts alike for studying perceived verticality under field conditions and raising awareness of dangerous misperceptions of verticality when body pitch and translational self-motion come together.

From Receptive to Perceptive Fields: Size-Dependent Asymmetries in Both Negative Afterimages and Subcortical On and Off Post-Stimulus Responses.

Negative afterimages are perceptual phenomena that occur after physical stimuli disappear from sight. Their origin is linked to transient post-stimulus responses of visual neurons. The receptive fields (RFs) of these subcortical ON- and OFF-center neurons exhibit antagonistic interactions between central and surrounding visual space, resulting in selectivity for stimulus polarity and size. These two features are closely intertwined, yet their relationship to negative afterimage perception remains unknown. Here we tested whether size differentially affects the perception of bright and dark negative afterimages in humans of both sexes, and how this correlates with neural mechanisms in subcortical ON and OFF cells. Psychophysically, we found a size-dependent asymmetry whereby dark disks produce stronger and longer-lasting negative afterimages than bright disks of equal contrast at sizes >0.8°. Neurophysiological recordings from retinal and relay cells in female cat dorsal lateral geniculate nucleus showed that subcortical ON cells exhibited stronger sustained post-stimulus responses to dark disks, than OFF cells to bright disks, at sizes >1°. These sizes agree with the emergence of center-surround antagonism, revealing stronger suppression to opposite-polarity stimuli for OFF versus ON cells, particularly in dorsal lateral geniculate nucleus. Using a network-based retino-geniculate model, we confirmed stronger antagonism and temporal transience for OFF-cell post-stimulus rebound responses. A V1 population model demonstrated that both strength and duration asymmetries can be propagated to downstream cortical areas. Our results demonstrate how size-dependent antagonism impacts both the neuronal post-stimulus response and the resulting afterimage percepts, thereby supporting the idea of perceptual RFs reflecting the underlying neuronal RF organization of single cells.SIGNIFICANCE STATEMENT Visual illusions occur when sensory inputs and perceptual outcomes do not match, and provide a valuable tool to understand transformations from neural to perceptual responses. A classic example are negative afterimages that remain visible after a stimulus is removed from view. Such perceptions are linked to responses in early visual neurons, yet the details remain poorly understood. Combining human psychophysics, neurophysiological recordings in cats and retino-thalamo-cortical computational modeling, our study reveals how stimulus size and the receptive-field structure of subcortical ON and OFF cells contributes to the parallel asymmetries between neural and perceptual responses to bright versus dark afterimages. Thus, this work provides a deeper link from the underlying neural mechanisms to the resultant perceptual outcomes.

The Serpentine Illusion: A Visual Motion Illusion Induced by Phase-Shifted Line Gratings.

In a pattern of horizontal lines containing ± 45° zigzagging phase-shifted strips, vivid illusory motion is perceived when the pattern is translated up or down at a moderate speed. Two forms of illusory motion are seen: [i] a motion "racing" along the diagonal interface between the strips and [ii] lateral (sideways) motion of the strip sections. We found the relative salience of these two illusory motions to be strongly influenced by the vertical spacing and length of the line gratings, and the period length of the zigzag strips. Both illusory motions are abolished when the abutting strips are interleaved, separated by a gap or when a real line is superimposed at the interface. Illusory motion is also severely weakened when equiluminant colored grating lines are used. Illusory motion perception is fully restored at < 20% luminance contrast. Using adaptation, we find that line-ends alone are insufficient for illusory motion perception, and that both physical carrier motion and line orientation are required. We finally test a classical spatiotemporal energy model of V1 cells that exhibit direction tuning changes that are consistent with the direction of illusory motion. Taking this data together, we constructed a new visual illusion and surmise its origin to interactions of spatial and temporal energy of the lines and line-ends preferentially driving the magnocellular pathway.

Stopping the rise of myopia in Asia.

This review discusses the rapid rise of myopia among school-age children in East and Southeast Asia during the last 60 years. It describes the history, epidemiology, and presumed causes of myopia in Asia, but also in Europe and the United States. The recent myopia boom is attributed primarily to the educational pressure in Asian countries, which prompts children to read for long hours, often under poor lighting and on computer screens. This practice severely limits the time spent outdoors and reduces exposure to sunlight and far vision. As a consequence, the eyes grow longer and become myopic. In a breakthrough study in Taiwan, it has been found that by increasing the time spent outdoors, the incidence of new myopia cases was reduced to half when children were sent onto the schoolyard for at least 2 h daily. This protection is attributed to the light-induced retinal dopamine, which blocks the abnormal growth of the eyeball. Once myopia has set in, low-dose atropine and orthokeratology have shown positive results in slowing myopia progression. Also, prismatic bifocal lenses and specially designed multifocal soft contact lenses have recently been tested with promising results. Treatment, however, must be initiated early as the disease progresses once it has started, thereby enhancing the risk for severe visual impairment and ultimately blindness.

Causal Evidence of Motion Signals in Macaque Middle Temporal Area Weighted-Pooled for Global Heading Perception.

Accurate heading perception relies on visual information integrated across a wide field, that is, optic flow. Numerous computational studies have speculated how local visual information might be pooled by the brain to compute heading, but these hypotheses lack direct neurophysiological support. In the current study, we instructed human and monkey subjects to judge heading directions based on global optic flow. We showed that a local perturbation cue applied within only a small part of the visual field could bias the subjects' heading judgments, and shift the neuronal tuning in the macaque middle temporal (MT) area at the same time. Electrical microstimulation in MT significantly biased the animals' heading judgments predictable from the tuning of the stimulated neurons. Masking the visual stimuli within these neurons' receptive fields could not remove the stimulation effect, indicating a sufficient role of the MT signals pooled by downstream neurons for global heading estimation. Interestingly, this pooling is not homogeneous because stimulating neurons with excitatory surrounds produced relatively larger effects than stimulating neurons with inhibitory surrounds. Thus our data not only provide direct causal evidence, but also new insights into the neural mechanisms of pooling local motion information for global heading estimation.

The collection of historical instruments at National Taiwan University.

This article presents three of the historical instruments from the National Taiwan University collection. The instruments were built between 1894 and 1902. The instruments are (1) Meumann's Largest Time Sense Apparatus, (2) Wundt's Pendulum Tachistoscope, and (3) Schumann's Wheel Tachistoscope. It is hoped that the presentation of these three historical instruments will serve a triple purpose: (a) to enable a greater appreciation of achievements of the scientists on whose shoulders we stand; (b) to illustrate the need for the time-consuming task of designing specialized apparatuses for a given experiment, typical at the time; and (c) to encourage a reflection on the mutual relationship between the instruments available, the questions asked, and the experiments done. In addition, the collection helps illuminate how the importation of apparatuses designed and built in Europe (Germany) to Taiwan and Japan contributed to the spread of Western psychology and its associated technologies on a global scale. (PsycINFO Database Record

Asymmetries of Dark and Bright Negative Afterimages Are Paralleled by Subcortical ON and OFF Poststimulus Responses.

Humans are more sensitive to luminance decrements than increments, as evidenced by lower thresholds and shorter latencies for dark stimuli. This asymmetry is consistent with results of neurophysiological recordings in dorsal lateral geniculate nucleus (dLGN) and primary visual cortex (V1) of cat and monkey. Specifically, V1 population responses demonstrate that darks elicit higher levels of activation than brights, and the latency of OFF responses in dLGN and V1 is shorter than that of ON responses. The removal of a dark or bright disc often generates the perception of a negative afterimage, and here we ask whether there also exist asymmetries for negative afterimages elicited by dark and bright discs. If so, do the poststimulus responses of subcortical ON and OFF cells parallel such afterimage asymmetries? To test these hypotheses, we performed psychophysical experiments in humans and single-cell/S-potential recordings in cat dLGN. Psychophysically, we found that bright afterimages elicited by luminance decrements are stronger and last longer than dark afterimages elicited by luminance increments of equal sizes. Neurophysiologically, we found that ON cells responded to the removal of a dark disc with higher firing rates that were maintained for longer than OFF cells to the removal of a bright disc. The ON and OFF cell asymmetry was most pronounced at long stimulus durations in the dLGN. We conclude that subcortical response strength differences between ON and OFF channels parallel the asymmetries between bright and dark negative afterimages, further supporting a subcortical origin of bright and dark afterimage perception.SIGNIFICANCE STATEMENT Afterimages are physiological aftereffects following stimulation of the eye, the study of which helps us to understand how our visual brain generates visual perception in the absence of physical stimuli. We report, for the first time to our knowledge, asymmetries between bright and dark negative afterimages elicited by luminance decrements and increments, respectively. Bright afterimages are stronger and last longer than dark afterimages. Subcortical neuronal recordings of poststimulus responses of ON and OFF cells reveal similar asymmetries with respect to response strength and duration. Our results suggest that subcortical differences between ON and OFF channels help explain intensity and duration asymmetries between bright and dark afterimages, supporting the notion of a subcortical origin of bright and dark afterimages.

Representation of illusory and physical rotations in human MST: A cortical site for the pinna illusion.

Visual illusions have fascinated mankind since antiquity, as they provide a unique window to explore the constructive nature of human perception. The Pinna illusion is a striking example of rotation perception in the absence of real physical motion. Upon approaching or receding from the Pinna-Brelstaff figure, the observer experiences vivid illusory counter rotation of the two rings in the figure. Although this phenomenon is well known as an example of integration from local cues to a global percept, the visual areas mediating the illusory rotary perception in the human brain have not yet been identified. In the current study we investigated which cortical area in the human brain initially mediates the Pinna illusion, using psychophysical tests and functional magnetic resonance imaging (fMRI) of visual cortices V1, V2, V3, V3A, V4, and hMT+ of the dorsal and ventral visual pathways. We found that both the Pinna-Brelstaff figure (illusory rotation) and a matched physical rotation control stimulus predominantly activated subarea MST in hMT+ with a similar response intensity. Our results thus provide neural evidence showing that illusory rotation is initiated in human MST rather than MT as if it were physical rotary motion. The findings imply that illusory rotation in the Pinna illusion is mediated by rotation-sensitive neurons that normally encode physical rotation in human MST, both of which may rely on a cascade of similar integrative processes from earlier visual areas. Hum Brain Mapp 37:2097-2113, 2016. © 2016 Wiley Periodicals, Inc.

Beyond the classical receptive field: The effect of contextual stimuli.

Following the pioneering studies of the receptive field (RF), the RF concept gained further significance for visual perception by the discovery of input effects from beyond the classical RF. These studies demonstrated that neuronal responses could be modulated by stimuli outside their RFs, consistent with the perception of induced brightness, color, orientation, and motion. Lesion scotomata are similarly modulated perceptually from the surround by RFs that have migrated from the interior to the outer edge of the scotoma and in this way provide filling-in of the void. Large RFs are advantageous to this task. In higher visual areas, such as the middle temporal and inferotemporal lobe, RFs increase in size and lose most of their retinotopic organization while encoding increasingly complex features. Whereas lower-level RFs mediate perceptual filling-in, contour integration, and figure-ground segregation, RFs at higher levels serve the perception of grouping by common fate, biological motion, and other biologically relevant stimuli, such as faces. Studies in alert monkeys while freely viewing natural scenes showed that classical and nonclassical RFs cooperate in forming representations of the visual world. Today, our understanding of the mechanisms underlying the RF is undergoing a quantum leap. What had started out as a hierarchical feed-forward concept for simple stimuli, such as spots, lines, and bars, now refers to mechanisms involving ascending, descending, and lateral signal flow. By extension of the bottom-up paradigm, RFs are nowadays understood as adaptive processors, enabling the predictive coding of complex scenes. Top-down effects guiding attention and tuned to task-relevant information complement the bottom-up analysis.

Asymmetries in blue-yellow color perception and in the color of 'the dress'.

The perception of color poses daunting challenges, because the light spectrum reaching the eye depends on both the reflectance of objects and the spectrum of the illuminating light source. Solving this problem requires sophisticated inferences about the properties of lighting and surfaces, and many striking examples of 'color constancy' illustrate how our vision compensates for variations in illumination to estimate the color of objects (for example [1-3]). We discovered a novel property of color perception and constancy, involving how we experience shades of blue versus yellow. We found that surfaces are much more likely to be perceived as white or gray when their color is varied along bluish directions, compared with equivalent variations along yellowish (or reddish or greenish) directions. This selective bias may reflect a tendency to attribute bluish tints to the illuminant rather than the object, consistent with an inference that indirect lighting from the sky and in shadows tends to be bluish. The blue-yellow asymmetry has striking effects on the appearance of images when their colors are reversed, turning white to yellow and silver to gold, and helps account for the variation among observers in the colors experienced in 'the dress' image that recently consumed the internet. Observers variously describe the dress as blue-black or white-gold, and this has been explained by whether the dress appears to be in direct lighting or shade (for example [5]). We show that these individual differences and potential lighting interpretations also depend on the special ambiguity of blue, for simply reversing the image colors causes almost all observers to report the lighter stripes as yellowish.

Asymmetrical color filling-in from the nasal to the temporal side of the blind spot.

The physiological blind spot, corresponding to the optic disk in the retina, is a relatively large (6 × 8°) area in the visual field that receives no retinal input. However, we rarely notice the existence of it in daily life. This is because the blind spot fills in with the brightness, color, texture, and motion of the surround. The study of filling-in enables us to better understand the creative nature of the visual system, which generates perceptual information where there is none. Is there any retinotopic rule in the color filling-in of the blind spot? To find out, we used mono-colored and bi-colored annuli hugging the boundary of the blind spot. We found that mono-colored annuli filled in the blind spot uniformly. By contrast, bi-colored annuli, where one half had a given color, while the other half had a different one, filled in the blind spot asymmetrically. Specifically, the color surrounding the nasal half typically filled in about 75% of the blind spot area, whereas the color surrounding the temporal half filled in only about 25%. This asymmetry was dependent on the relative size of the half rings, but not the two colors used, and was absent when the bi-colored annulus was rotated by 90°. Here, the two colors on the upper and lower sides of the blind spot filled in the enclosed area equally. These results suggest that the strength of filling-in decreases with distance from the fovea consistent with the decrease of the cortical magnification factor.

Receptive fields of visual neurons: the early years.

This paper traces the history of the visual receptive field (RF) from Hartline to Hubel and Wiesel. Hartline (1938, 1940) found that an isolated optic nerve fiber in the frog could be excited by light falling on a small circular area of the retina. He called this area the RF, using a term first introduced by Sherrington (1906) in the tactile domain. In 1953 Kuffler discovered the antagonistic center-surround organization of cat RFs, and Barlow, Fitzhugh, and Kuffler (1957) extended this work to stimulus size and state of adaptation. Shortly thereafter, Lettvin and colleagues (1959) in an iconic paper asked "what the frog's eye tells the frog's brain". Meanwhile, Jung and colleagues (1952-1973) searched for the perceptual correlates of neuronal responses, and Jung and Spillmann (1970) proposed the term perceptive field (PF) as a psychophysical correlate of the RF. The Westheimer function (1967) enabled psychophysical measurements of the PF center and surround in human and monkey, which correlated closely with the underlying RF organization. The sixties and seventies were marked by rapid progress in RF research. Hubel and Wiesel (1959-1974), recording from neurons in the visual cortex of the cat and monkey, found elongated RFs selective for the shape, orientation, and position of the stimulus, as well as for movement direction and ocularity. These findings prompted the emergence in visual psychophysics of the concept of feature detectors selective for lines, bars, and edges, and contributed to a model of the RF in terms of difference of Gaussians (DOG) and Fourier channels. The distinction between simple, complex, and hypercomplex neurons followed. Although RF size increases towards the peripheral retina, its cortical representation remains constant due to the reciprocal relationship with the cortical magnification factor (M). This constitutes a uniform yardstick for M-scaled stimuli across the retina. Developmental studies have shown that RF properties are not fixed. RFs possess their full response inventory already at birth, but require the interaction with appropriate stimuli within a critical time window for refinement and consolidation. Taken together these findings paved the way for a better understanding of how objective properties of the external world are encoded to become subjective properties of the subjective, perceptual world.

Neon color spreading in dynamic displays: temporal factors.

When a red star is placed in the middle of an Ehrenstein figure so as to be collinear with the surrounding black rays, a reddish veil is perceived to fill the white center. This is called neon color spreading. To better understand the processes that give rise to this phenomenon, we studied the temporal properties of the effect. Specifically, we presented a "sustained" black Ehrenstein figure (rays) for 600 ms and a "transient" red star for 48 ms, or the converse pattern, at various stimulus onset asynchronies (-100-700 ms) and asked subjects to compare the strength of the neon color in the test stimulus to that of a reference pattern in which the transient star had an onset asynchrony of 300 ms. Additional exposure durations of 24 and 96 ms were used for each transient stimulus in order to study the effect of temporal integration. Simultaneity of the on- and off-transients of the star and the Ehrenstein rays were found to optimize neon color spreading, especially when both stimuli terminated together. Longer exposure durations of the transient stimulus up to 96 ms further improved the effect. Neon color spreading was much reduced when the transient stimulus was presented soon after the beginning of the sustained stimulus, with a gradual build-up towards the end. These results emphasize the importance of stimulus onset asynchrony (SOA) and stimulus termination asynchrony (STA) for the perception of neon color spreading.

The Ouchi-Spillmann illusion revisited.

In a disk-ring pattern composed of horizontally oriented checks in the centre and vertically oriented checks in the surround, the centre appears to slide relative to the surround when the pattern is slowly moved about. This phenomenon has been called the Ouchi illusion. Slow sliding movements may represent involuntary ocular drifts, while occasional jerks suggest a contribution by microsaccades. The conditions under which the illusion occurs both with free viewing and in the absence of involuntary eye movements are reviewed. Illusory sliding is most pronounced with diagonal movement of the stimulus pattern, resulting in apparent motion orthogonal to the orientation of the disk. The illusion requires checks of low spatial frequency; it persists with low luminance contrast and blur of the inducing pattern, but is absent at equiluminance. These results suggest a magnocellular neuronal mechanism. Sliding continues to be seen with an empty annular zone separating centre and surround, and is seen even when there is no concentric surround at all, just two abutting flanks. Nine hypotheses proposed to account for the illusory motion of the centre relative to the surround are reviewed. Among these the models based on an integration bias of local motion vectors (Mather 2000 Perception 29 721-727) and Type II plaid motion (Ashida2002 Vision Research 42 1413-1420) come closest to explaining illusory sliding in the Ouchi figure, but open questions remain. Specifically, more research is warranted to correlate the predicted with the perceived direction of sliding motion in both check and grating patterns.