The relationship between sighting dominance and the fading of a stabilized retinal image

The fading of a stabilized retinal image in the sighting and the nonsighting dominant eye was studied using the Haidinger’s brush target. Reaction time to the complete disappearance of the stabilized image was significantly longer when the target was input to the sighting eye. The greater persistence of stabilized targets in the sighting eye suggests possible differences in the neural channels from the two eyes or processing differences in the two monocular channels that are related behaviorally to eye dominance.     

Monocular asymmetries in recognition after an eye movement: Sighting dominance and dextrality

Although monocular recognition scores for targets presented immediately after an eye movement do not differ, the two eyes show marked recognition asymmetries when both eyes are receiving inputs but a specific target is only presented to one. In general, the right eye performs better than the left, although there are interactions with sighting dominance and the direction of eye movement.     

Eye movements and decrement in the Oppel-Kundt illusion

Two groups of 15 Ss each observed the Oppel-Kundt illusion, in which a divided extent appears longer than an undivided extent. The group which made saccadic eye movements over the figure showed significant decrement of the illusion, while the group which maintained steady fixation showed no decrement. These results support an interpretation which maintains that information from eye-movement errors provides data as to the nature and extent of the illusion, thus leading to decrement.     

Decrement of the Müller-Lyer and Poggendorff illusions: the effects of inspection and practice

Five experiments assessed the decline or decrement in illusion magnitude for the wings-out form and the combined or Brentano form of the Müller-Lyer illusion, and for the Poggendorff illusion. Judgments were obtained under conditions of either continuous or intermittent inspection of the illusion figure. In the continuous-inspection conditions observers scanned the illusion figure during the inter-trial intervals whereas in the intermittent-inspection conditions they did not. Substantial illusion decrement was found in all continuous-inspection conditions and in intermittent conditions with short inter-trial intervals (upto 20 s) but not with longer inter-trial intervals. However, intermittent-inspection with a long inter-trial interval (40 s) produced illusion decrement but only when observers were instructed during the decrement session to ignore the wings, and pay attention to the shaft, of the Müller-Lyer figure. Taken together, the pattern of results does not support the claim that illusion decrement is primarily a product of practice or repeated trials.     

Lateralized interhemispheric transfer of color cues: evidence for dynamic coding principles of visual lateralization in pigeons

Visual feature discrimination tasks in pigeons reveal a right eye/left hemisphere dominance at the population level. Anatomical studies and lesion data show this visual lateralization to be related to asymmetries of the tectofugal system, which ascends from the tectum over the n. rotundus to the forebrain. Anatomically, this system is characterized by numerous morphological and connectional asymmetries which result in a bilateral visual representation in the dominant left hemisphere and a mostly contralateral representation in the subdominant right hemisphere. Ontogenetically, visual lateralization starts with an asymmetrical embryonic position within the egg, which leads to asymmetries of light stimulation. Differences in exposure to light stimulation between the eyes result in activity differences between the ascending tectofugal pathways of the left and the right hemisphere, which are transcribed during a critical time span into morphological asymmetries. The asymmetries established after this transient period finally start to determine the lateralized processes of the visual system for the entire life span of the individual. We now can show that these anatomical lateralizations are accompanied by asymmetries of interocular transfer, which enable a faster shift of learned color cues from the dominant right to the left eye than vice versa. In summary, our data provide evidence that cerebral asymmetries are based both on "static" anatomical and on "dynamic" process-dependent principles.     

Fragmentation of monocular afterimages in individuals with and without normal binocular vision

Monocular afterimages of a vertical line were generated in each eye of binocularly normal individuals and of those lacking binocular single vision or stereopsis as a consequence of childhood strabismus. Fragmentations and disappearances of the afterimages occurred less frequently in the strabismic than in the normal subjects; they were also less frequent in the dominant (nonamblyopic) eyes of the strabismics than in their amblyopic eyes. The afterimages remained visible for longer when presented to the dominant eyes of the strabismic subjects, and a similar effect was found between the sighting dominant and nondominant eyes of normal subjects.     

Visual-geometric illusions: unisex phenomena

The possibility of sex differences in responses to visual-geometric illusions was investigated with the use of forty-five illusion variants and a sample of 221 observers. No difference in illusion magnitude as a function of sex was found. A second experiment measured illusion decrement and transfer of decrement to other illusion configurations. Again there were no significant differences between male and female observers.     

Yang's iris illusion: External contour causes length‐assimilation illusions1

The Delboeuf illusion and the Ebbinghaus illusion (also known as the Titchener illusion) demonstrate that an external contour can lead to size‐assimilation and size‐contrast perception. This paper explores a novel illusion, revealing that neighboring external contours can also lead to a distortion in length perception. The illusion was originally discovered from a face stimulus (Experiment 1) in which a face was depicted alongside its mirror image so as to make the four irises absolutely equidistant. The distance between the middle two irises was underestimated in Asian faces, but overestimated in Caucasian faces. The illusion was also maintained when the facial stimuli were replaced by line drawings of eyes (Experiment 2). However, the illusion vanished when the irises were presented alone. Further scrutiny of the differences in facial characteristics between Asian and Caucasian faces reveals that the illusion might be elicited by the relative position of the eye shapes. This hypothesis was confirmed in Experiment 3, in which the distances between the eye shapes and the irises were manipulated.     

Decrement of the Müller-Lyer illusion with saccadic and tracking eye movements

Subjects viewed the Müller-Lyer illusion, making either saccadic or smooth tracking eye movements between the apexes of the arrow heads. The decrement in the magnitude of the illusion was significantly greater for Ss in the saccadic viewing condition. Saccadic and smooth tracking eye movements are separately controlled,and information about eye position is more readily available from the efferent signals issued to control a saccadic eye movement. The experimental findings were consistent with the hypothesis that Ss in the saccadic condition learned a new afferent efferent association. The results support a theory that visual perception is determined by efferent readiness activated by visual afferent stimulation.     

Mueller-Lyer decrement: practice or prolonged inspection?

Noting the similarity between the illusion decrement and selective adaptation paradigms, Long has challenged the view that illusion decrement effects reflect a strategic--as opposed to a structural--underlying mechanism, and has called for further research on this issue. To investigate the confound between prolonged free inspection and repeated trials in the standard decrement procedure, the effects of three inspection conditions (continuous, intermittent, and immediate) on the magnitude of the overestimation Mueller-Lyer illusion have been assessed under two levels of trials (a total of two or six judgments). Significant illusion decline was found only under conditions of repeated trials, with either continuous or intermittent inspection. These findings do not support the predictions of purely structural theories (including neural adaptation and efferent readiness theories), according to which degree of decrement should be determined solely by viewing time. Instead, the data demonstrate that illusion decrement is a product of practice, providing converging evidence for the view of decrement as involving a cognitive 'recalibration' or learning process.     

Inability to wink an eye and eye dominance.

Data from 56 subjects in Grades 4 to 12 only able to wink one eye indicated that the non-winking eye was used as the dominant one in tests on monocular and binocular sighting.     

Assimilation and contrast illusions: Differences in plasticity

Three experiments show differences in the plasticity of the contrast and assimilation portions of the Delboeuf, Ebbinghaus, and Ponzo illusions. Contrast illusions show decrement in illusion magnitude with free inspection, whereas assimilation illusions do not. A model to explain both the original distortion and the differential susceptibility of the two classes of illusion to decrement is offered.     

Six-month-old infants perceive the hollow-face illusion

In this study we investigated infants' perception of the hollow-face illusion. 6-month-old infants were shown a concave mask under monocular and binocular viewing conditions and the direction of their reaches toward the mask was recorded. Adults typically perceive a concave mask as convex under monocular conditions but as concave under binocular conditions, depending on viewing distance. Based on previous findings that infants reach preferentially toward the parts of a display that are closest to them, we expected that, if infants perceive the hollow-face illusion as adults do, they would reach to the center of the mask when viewing it monocularly and to the edges when viewing it binocularly. The results were consistent with these predictions. Our findings indicated that the infants perceived the mask as convex when viewing it with one eye and concave when viewing it with two eyes. The results show that 6-month-old infants respond to the hollow-face illusion. Our finding suggests that, early in life, the visual system uses the constraint, or assumption, that faces are convex when interpreting visual input.     

Horizontal-vertical illusion: continuous decrement or the deviant first guess?

Numerous studies have reported that repetitive or extensive inspection leads to short-term decrement of the horizontal-vertical illusion. The present experiment explored whether this decrement reflects a gradual decline, as previously assumed, or is better described as a singular drop-off beyond the initial evaluation. 111 student participants adjusted vertical or horizontal lines such that they appeared equally long with a perpendicular standard. There were 8 successive adjustment trials for each subject. The results suggest that a substantial component of the illusion depends on the first impression assessment. The earlier anatomical and cognitive theories of the horizontal-vertical illusion cannot incorporate this datum. However, recent findings suggest that a motor theory of illusion might accommodate the observed one-step decrement in the illusion.     

Vertical-horizontal illusion: One eye is better than two

The vertical-horizontal illusion is the tendency for observers to overestimate the length of a vertical line relative to a horizontal line that has the same length. One explanation of this illusion is that the visual field is elongated in the horizontal direction, and that the vertical-horizontal illusion is a kind of framing effect (Künnapas, 1957a, 1957b, 1957c). Since the monocular visual field is less asymmetric than the combined visual field, this theory predicts that the illusion should be reduced with monocular presentation. This prediction was tested in five experiments, in which the vertical-horizontal illusion was examined in a variety of situations—including observers seated upright versus reclined 90°, monocular presentation with the dominant versus the nondominant eye, viewing in the dark versus in the light, and viewing with asymmetrical frames of reference. The illusion was reliably reduced with monocular presentation under conditions that affected the asymmetry of the phenomenal visual field.     

The eyes or the mouth? Feature salience and unfamiliar face processing in Williams syndrome and autism

Using traditional face perception paradigms the current study explores unfamiliar face processing in two neurodevelopmental disorders. Previous research indicates that autism and Williams syndrome (WS) are both associated with atypical face processing strategies. The current research involves these groups in an exploration of feature salience for processing the eye and mouth regions of unfamiliar faces. The tasks specifically probe unfamiliar face matching by using (a) upper or lower face features, (b) the Thatcher illusion, and (c) featural and configural face modifications to the eye and mouth regions. Across tasks, individuals with WS mirror the typical pattern of performance, with greater accuracy for matching faces using the upper than using the lower features, susceptibility to the Thatcher illusion, and greater detection of eye than mouth modifications. Participants with autism show a generalized performance decrement alongside atypicalities, deficits for utilizing the eye region, and configural face cues to match unfamiliar faces. The results are discussed in terms of feature salience, structural encoding, and the phenotypes typically associated with these neurodevelopmental disorders.     

Hans Gertz revisited: the different effects of invisibility and darkness on pursuit eye movements.

Subjects were required to track their self-moved hands with smooth eye movements in total darkness. The effect of holding transparent and opaque screens between the eyes and the hand upon pursuit eye movements was examined. Opaque screens produced a significant decrement in pursuit when the eye was moving in a direction in which it was generally less efficient at making smooth eye movements.     

The eyes or the mouth? Feature salience and unfamiliar face processing in Williams syndrome and autism

Using traditional face perception paradigms the current study explores unfamiliar face processing in two neurodevelopmental disorders. Previous research indicates that autism and Williams syndrome (WS) are both associated with atypical face processing strategies. The current research involves these groups in an exploration of feature salience for processing the eye and mouth regions of unfamiliar faces. The tasks specifically probe unfamiliar face matching by using (a) upper or lower face features, (b) the Thatcher illusion, and (c) featural and configural face modifications to the eye and mouth regions. Across tasks, individuals with WS mirror the typical pattern of performance, with greater accuracy for matching faces using the upper than using the lower features, susceptibility to the Thatcher illusion, and greater detection of eye than mouth modifications. Participants with autism show a generalized performance decrement alongside atypicalities, deficits for utilizing the eye region, and configural face cues to match unfamiliar faces. The results are discussed in terms of feature salience, structural encoding, and the phenotypes typically associated with these neurodevelopmental disorders.     

Visual stimuli for strabismic suppression

The effects of orientation and spatial frequency of grating stimuli upon suppression were examined with a binocular rivalry paradigm in a group of ten strabismic patients and in a control normal group. Duration, frequency, and period of rivalry were examined as functions of differences in orientation and spatial frequency of dichoptic achromatic sinusoidal gratings. Records were made of responses by the sighting and by the nonsighting eye as well as responses during periods of combined binocular vision. Strabismic subjects reported normal binocular rivalry when presented with gratings of dissimilar orientation. Suppression of the deviating eye in strabismic subjects occurred with stimuli of similar orientation and was unaffected by spatial-frequency differences between dichoptic stimuli. Suppression was most intense under conditions that normally stimulate stereopsis and sensory fusion.     

Comparative neuropsychology of the dual brain: a stroll through animals' left and right perceptual worlds

Perceptual asymmetries in humans typically manifest themselves under quite unnatural settings (e.g., tachistoscopic viewing and dichotic listening) and this has put into question their real biological significance. In animals with laterally placed eyes, however, perceptual asymmetries are ubiquitous in the normal, everyday behavior, as revealed by the differential use of the lateral visual field of the left and right eye in a variety of tasks. Data are presented showing how preferential use of the left and right eyes influences visual discrimination learning and detour behavior in chicks; similarities with detour tests performed in fish and evidence for asymmetries in eye use in animals with larger binocular overlap (e.g., anuran amphibians) are discussed. Implications of these perceptual asymmetries on the formation and fate of memory traces are put forward, with examples from unihemispheric sleep and lateralization of spatial memory in chicks. Finally, speculations about the evolutionary origins and possible adaptive advantages of perceptual asymmetries in vertebrates are presented.