Apparent head position as a basis for a visual aftereffect of prolonged head tilt

A possible explanation of the visual spatial aftereffect following head tilt with eyes closed is that it is an outcome of a proprioceptive aftereffect of head position. If the upright head is apparently tilted then it might be expected that a vertical line in a dark room would also be apparently tilted. This explanation predicts that the direction and magnitude of the visual and proprioceptive aftereffects would correspond. The second of two experiments showed that the trends of the two aftereffects as a function of head tilt angle were different. It was concluded that the visual aftereffect cannot be explained in terms of a proprioceptive aftereffect.     

Involvement of neck proprioceptive system in visual after-effect from prolonged head tilt

Judgements of object orientation after prolonged head tilt differ relative to those made before tilt. This visual spatial after-effect was investigated with lateral head tilt relative to the upright and supine body. The data from two experiments indicate that the magnitude and direction of the visual after-effect does not differ under the two body postures. It is concluded that the proprioceptive system of the neck, as opposed to the otolith system of the utricle, is involved in the after-effect.     

Selective visual attention modulates the direct tilt aftereffect

One's being able to allocate attention to particular regions or properties of the visual field is fundamental to visual information processing. Visual attention determines what input is carefully analyzed and what input is more or less ignored. But at what stage of the visual system is this process evident? We describe three experiments that demonstrate an effect of voluntary spatial attention and voluntary object-based attention on an orientation illusion (the tilt aftereffect) that is believed to take place in primary visual cortex. This finding, in which selective visual attention influences adaptation to visual orientation information, contributes to mounting evidence for a view of visual perception in which mutual interaction takes place between high-level and low-level subsystems.     

Effect of prolonged tilt on visual orientation

Visual orientation during lateral tilt is viewed in terms of orientation constancy. The postural systems involved in the maintenance of constancy are considered to be those of the otolith, neck and trunk. The relative contribution of these systems was investigated by obtaining visual verticality judgments immediately upon and several minutes after head, body, and trunk tilts. Due to the apparent non-adaptation of the otolith system any changes in visual orientation resulting from prolonged tilt would be attributed to adaptation of the proprioceptive system stimulated. For 30° head tilt visual orientation over-constancy was reduced by about 2°, reflecting the influence of the neck system. Prolonged body tilts of 30°, 60° and 90° reduced the constancy operating by approximately 1°, 3° and 8°, respectively. This was taken to indicate the contribution of the trunk system, which increased with increasing degrees of body tilt. The above interpretations received strong support from experiments involving trunk tilt, which stimulates only the neck and trunk systems.     

视时距知觉适应后效的空间选择性

时距知觉适应后效是指长时间适应于某一特定时距会导致个体对后续时距产生知觉偏差。其中对视时距知觉适应后效空间选择性的探讨存在争议,有研究支持位置不变性,也有研究支持位置特异性。这类研究能有效揭示时距编码的认知神经机制,位置不变性可能意味着时距编码位于较高级的脑区,而位置特异性则可能意味着时距编码位于初级视觉皮层。未来还可以探究时距知觉适应后效的视觉坐标表征方式,开展多通道研究以及相应的神经基础研究。     

The perception of verticality and the frame of reference of the visual tilt aftereffect

Previous research has suggested that the visual tilt aftereffect operates according to a gravitational frame of reference. Three experiments were conducted to test this conclusion further. In each experiment, observers (with head upright) adjusted an illuminated bar to apparent vertical following various adaptation conditions. In Experiment 1, observers were given clear visual cues for objective vertical while adjusting the bar. In Experiment 2, they were not given visual cues for vertical. The adaptation conditions in Experiments 1 and 2 consisted of various combinations of head and stimulus tilt. Experiment 3 investigated the effects of head tilt alone. The results indicated that the tilt aftereffect follows a retinal frame of reference under some conditions (Experiment 1) and appears to follow a gravitational frame under others (Experiment 2). These results can be predicted by a simple model involving two factors, a purely visual aftereffect that follows a retinal frame and an extravisual aftereffect that appears to follow a gravitational frame.     

Apparent body tilt and postural aftereffect

Apparent orientation of the body tilted laterally in the frontal plane was studied with the methods of absolute judgments in four experiments. In Experiment 1, 17 subjects, who maintained the normal adaptation of body to gravity, estimated their body tilts under the condition of seeing the gravitational vertical and under the condition of eliminating it. The results showed that (1) there was not a significant difference between the two conditions and (2) the small tilts of less than 45° were exactly estimated, whereas the large tilts of 45°–108° were overestimated. In Experiment 2,10 subjects estimated their body tilts under three velocities of a rotating chair on which each subject was placed. Although both body tilt and chair velocity were found to influence tilt estimation, the effect of body tilt was overwhelmingly greater than that of chair velocity. In Experiment 3, 11 subjects adapted their bodies to a 72° left tilt for 10 min and then estimated various body tilts around the adapting tilt. The estimations obtained under the 72° adaptation were lower than those obtained under the 0° adaptation, and this reduction was greater for the test tilt that was farther away from the adapting tilt. In Experiment 4, 11 subjects adjusted their own body tilts to designated angles. The results confirmed the outcomes of absolute estimation in Experiments 1-3. From these findings and past literature, the judgments of body tilt were considered to be subserved by a single sensory process that was based on the cutaneous and muscular proprioceptors, rather than the vestibular and joint proprioceptors.     

The retinal reference of the tilt aftereffect

Day and Wade (1969) proposed that visual “normalization” and the visual tilt aftereffect depend upon the gravitational orientation of test and inducing figures and that the retina! orientation of these figures is irrelevant. Their failure to distinguish between “normalization” and aftereffect is pointed out, and an analysis of their experiment suggested that it could not yield data which would unambiguously support either the gravitational or the retinal viewpoint. An experiment was reported in which a tilt aftereffect was found to occur under conditions where inducing and test figures could not vary in gravitational orientation. It was concluded that retinal orientation is a sufficient factor in the tilt aftereffect situation; whether it is a necessary factor or whether gravitational orientation is also sufficient remains to be determined.     

A motion aftereffect from visual imagery of motion

Mental imagery is thought to share properties with perception. To what extent does the process of imagining a scene share neural circuits and computational mechanisms with actually perceiving the same scene? Here, we investigated whether mental imagery of motion in a particular direction recruits neural circuits tuned to the same direction of perceptual motion. To address this question we made use of a visual illusion, the motion aftereffect. We found that following prolonged imagery of motion in one direction, people are more likely to perceive real motion test probes as moving in the direction opposite to the direction of motion imagery. The transfer of adaptation from imagined to perceived motion provides evidence that motion imagery and motion perception recruit shared direction-selective neural circuitry. Even in the absence of any visual stimuli, people can selectively recruit specific low-level sensory neurons through mental imagery.     

Eye-position aftereffects of backward head tilt manifested by illusory visual direction

Three experiments showed posttest-minus-pretest shifts in subjective straight-ahead eye position when subjects read for 3, 6, or 9 min with their heads tilted back 20° from upright. These shifts were significant relative to control conditions in which subjects read with their heads upright. All subjects read with the same straight-ahead eye-in-head position. Variability-reducing procedures were developed to provide better measures over Experiments 1, 2. and 3. Explanations in terms of deliberate compensation, head-position asymmetries, eye-position asymmetries, and progressive error were ruled out. It was hypothesized that the shifts were caused by negative aftereffects of compensation for the doll reflex. The doll reflex rotates the eyes down without central registration. causing an upward illusory shift of visual direction similar to what is caused by wedge prisms. Perceptual-motor adaptation to this shift, i.e., doll adaptation, causes an illusory shift in the opposite direction when the head is returned to upright.     

Egocentric localization of the visual horizontal in normal and labyrinthine-defective observers as a function of head and body tilt

Perception of the visual horizontal by observers in five different combinations of head and body position was studied to determine the effect of 20-degree body tilts. Both normal and labyrinthine-defective observers made five settings to the visual horizontal for each condition using, a goggle device which presented a collimated line of light to the right eye while the other eye was covered. The results showed no significant constant errors in the settings by either group, and it is suggested that the absence of the E-phenomenon was due primarily to adequate contact cues and kinesthetic cues. The data also make it clear that vestibular information is not required for veridical perception of the visual horizontal under these experimental conditions.     

An increase in strength of tilt aftereffect associated with tryptophan depletion

The effects of a tryptophan-free amino acid mixture on tilt aftereffect, movement aftereffect, and the Mueller-Lyer illusion were studied. 12 male subjects ingested either a balanced amino acid mixture or a tryptophan-free mixture which causes a marked depletion of brain tryptophan and serotonin. The tryptophan-free mixture significantly increased the strength of tilt aftereffect but had no effect on movement aftereffect or the Mueller-Lyer illusion. These results were discussed with reference to the pharmacological activity of serotonin and its influence on the strength of lateral inhibition in mammalian brains.     

A three-dimensional motion aftereffect produced by prolonged adaptation to a rotation simulation

After adaptation to a perspective simulation of a square plane rotating in depth, an ambiguous rotation simulation (ie one containing no perspective information) appears to rotate in the direction opposite that of adaptation. The strength of this three-dimensional motion aftereffect (MAE) is proportional to the amount of perspective available in the adaptation display and, in the dark, decays to about 75% of its initial strength within about 546 s. The nature of the testing situation and a control experiment suggest that the three-dimensional MAE is not caused by retinal adaptation of two-dimensional directionally selective mechanisms.     

Interactions between spatial and kinetic dimensions in movement aftereffect

In some conditions, the surface of the test figure on which one sees an aftereffect of movement does not fit with that part of the visual field previously adapted to a movement. Such an effect, called kinetic-figural effect, may be conceived of as resulting from an interaction between two perceptual systems, each one giving specific information: one for the kinetic aspects which are spatially defined, the other for the spatial relationship inside the visual field. Experiments are presented which indicated the validity of a “law of location” for a movement aftereffect, together with some effects of the spatial relationships between adapting and test fields upon the movement aftereffect.