Changes of visual fields in intracranial tumors outside the cerebral hemispheres]

Based on neurosurgical material of 1,746 brain tumours, the changes of the visual field determined by isopteric perimetry are discussed with their significe with regard to tumours of corpus callosum, lateral ventricles, brain stem ganglia, IIIrd ventricle, region of the sella and adjacent areas as well as posterior fossa. The proportion of unilateral blindness with primary opticus atrophy and of skotomas is strinkingly high, so that in cases of loss of vision, not readily explicable by ophthalmology, as well as in unilateral defects of the visual field, intracranial processes must be thought of.     

Pathological visual field and brain tumor]

The general relationships between an operatively or autoptically localized tumor and the visual field determined by means of ikineticer perimetry are investigated, the patient stock being a total of 1756 neurosurgical brain-tumor inpatients. Examination of the visual field was possible with four fifths of the brain-tumor patients. Hemianopic, quadrantanopsic, or scotomatous defects of a topically localizable nature could be found in almost one third of the total patient stock available for examination. The clinically particularly interesting criteria of localization of homonymous-hemianopsia defects such as macular sparing and incongruence/congruence of visual field changes should be of no importance to the localization within the visual pathway of brain-tumor patients.     

Changes in cerebral metabolism during experimental anuria]

After experimental ureterotomy in mice, the changes which occurred in cerebral metabolism were studied. A significant increase in the cerebral glucose and glycogen level as well as of degradation power was noticed 25 hours after the operation. The level of lactic acid production in the same period of renal insufficience indicated a gradual decreasing tendency. These results as well as further details are discussed with regard to the underlying disturbances.     

Increasing the benefits of eye-tracking devices in divided visual field studies of cerebral asymmetry

A wide range of methods has been proposed for ensuring central fixation in divided visual field studies of cerebral asymmetry. We present some of the problems associated with ensuring central fixation and argue that objectively monitoring fixation location with an eye-tracking device can provide the only accurate and, therefore, acceptable technique. However, the mere use of this equipment does not overcome all of the problems associated with controlling fixation location, and previous studies have overlooked the importance of providing feedback on fixation accuracy and the role of visual attention. We propose a straightforward method of accommodating both these influences in studies using eyetracking devices to control fixation location.     

Measurement of the visual field

There is increasing evidence that concurrent visual and nonvisual tasks not only reduce the size but also result in systematic deformation of the visual field. Given such complex changes in the visual field, appropriate representation and measurement of its shape is all important. Shape measures utilized by researchers and reported in the literature should also be sufficiently standardized to allow comparison of results across experiments.     

Evidence for stimulus-response compatibility effects in a divided visual field study of cerebral lateralization

The question addressed here was whether lateral asymmetry of processing might be influenced by response position, a factor which is usually considered irrelevant in divided visual field studies of cerebral lateralization. For this purpose a lexical decision task, which had previously been investigated with lateral unimanual two-finger choice reactions (Heister et al. 1983), was carried out under different manual and vocal response conditions so as to uncover possible S-R compatibility effects. In the first study, thirty-two subjects responded unimanually, with their responding hand held in a medial position. In the second study, twenty-four subjects responded vocally, i.e., in both cases the spatial (right/left) cues of the response position were eliminated. The reaction time advantage for compatible S-R pairings obtained with lateral hand position disappeared in the experiment with medial hand position, and the right-field superiority for vocal reactions was much smaller than the right-field superiority for right-hand reactions in the earlier lateral experiment. This indicates that an S-R compatibility effect contributed to the results of the earlier experiment. Thus, S-R compatibility can affect even unimanual reactions in lateralization studies.     

Development of the functional visual field

Andries Sanders' dissertation examined selective mechanisms in the functional visual field, and much of his work since has been concerned with the stages that underlie visual information processing particularly while making saccades. We argue that the study of orienting in the functional visual field is timely because it deals with the relation of covert attention shifts, eye movements and head movements to their underlying neurology. In our paper we develop a method to study learning of sequences at all ages from infants to adults. Our studies focus on how learning influences anticipatory eye movements. We examined the learning of unambiguous and context dependent sequences by 4-, 10-, and 18-month-old infants and undergraduates. We found clear learning of unambiguous sequences at 4 months, but learning of context dependent associations was found only in 18-month-olds and in adults. We hypothesize that the learning of unambiguous sequences by 4-month-olds reflects maturation of a basal ganglia-parietal circuit related to adult implicit learning, while the learning of context dependent sequences requires development of frontal structures underlying more general attentional abilities.     

Brightness perception in the visual field

Summary Apparent brightness was measured at different positions in the visual field for scotopic, mesopic, and photopic adaptation levels by means of a magnitude estimation technique. Apparent brightness of targets with a given luminance remained rather constant throughout the visual field for the mesopic and photopic adaptation level; for the scotopic adaptation level targets in the foveal and perifoveal area had to be more intense in order to appear as bright as targets in the far periphery (beyond 20° eccentricity). For the photopic range, two brightness power functions with different exponents were obtained for the luminance range from 1 to 100 mL at each eccentricity. The exponent for the range from 1 to 10 mL is considerably greater than the exponent beyond 10 mL, and appears to increase with increasing eccentricity.The experiments described in this paper were partly supported by Deutsche Forschungsgemeinschaft and SFB 50-C 6.     

Sensorimotor expectations and the visual field

Sensorimotor expectations concern how visual experience covaries with bodily movement. Sensorimotor theorists argue from such expectations to the conclusion that the phenomenology of vision is constitutively embodied: objects within the visual field are experienced as 3-D because sensorimotor expectations partially constitute our experience of such objects. Critics argue that there are (at least) two ways to block the above inference: to explain how we visually experience objects as 3-D, one may appeal to such non-bodily factors as (1) expectations about movements of objects, not the perceiver, or to (2) the role of mental imagery in visual experience. But instead of using sensorimotor expectations to explain how objects are experienced within the visual field, we can instead use them to explain our experience of the visual field itself and, in particular, our experience of its limits; that is, our ever-present visual sense of there being more to see, beyond what’s currently within the visual field. Crucially, this inference from sensorimotor expectations to the constitutive embodiment of visual phenomenology is not threatened by the above two challenges. I thus present here a sensorimotor theory of the phenomenology of the visual field, that is, our experience of our visual fields as such.

     

Figural preference and the visual field

Three experiments tested a hypothesis that the shape and relative dimensions of the binocular visual field determine a preference for rectangles possessing dimensions similar to those of the golden section. The results were that Ss horizontally oriented the rectangles they had drawn in correspondence with the shape of the binocular visual field but when Ss chose the most pleasing rectangles there was no significant preference for rectangles whose long side was horizontal. For all experiments there was little preference for rectangles whose ratio of short to long side approximated the golden section. There was some evidence that the placement of the rectangles with respect to the background affects preference.     

Allocation of attention in the visual field

This research investigated whether attentional resources can be simultaneously allocated to several locations in a visual display, whether the mode of processing (serial or parallel) can be switched within a trial, and the nature of the costs when attentional resources are concentrated on an invalid location. Subjects were required to determine which of two target letters was present in eight-letter circular displays. In precue conditions, a primary and a secondary target location were designated 150 ms before target onset by an indicator that varied in validity. In the control conditions no cue was provided. A second experiment verified several assumptions that had been made in interpreting the data of Experiment 1. Modifications in Jonides' (1983) two-process model were suggested in terms of a zoom lens model of attentional resources. Instead of two alternative processing modes, attentional resources are conceived as capable of distribution over the visual field, but with low resolving power, or as continuously constricting to small portions of the visual field with a concomitant increase in processing power.     

Movements of attention across the visual field

Vocal reaction times were measured for targets presented at three distances from fixation. The targets were preceded by a cue, and the time interval between the cue and the target (stimulus-onset asynchrony; SOA) was varied. For each peripheral distance, the reaction time function initially declined as SOA was increased and then reached asymptote. The further the target from fixation, the longer the SOA at which the function reached asymptote. The asymptotic SOA values were taken as a measure of the time it takes attention to reach a given target. Comparisons of these values for the three peripheral distances permitted estimating the velocity of attention movements. These measurements suggest that when summoned by a peripheral cue, attention travels through space at a constant velocity of about 1 degree per 8 msec.     

The visual light field

Human observers are sensitive to the '(physical) light field' in the sense that they have expectations of how a given object would appear if it were introduced in the scene in front of them at some arbitrary location. Thus the 'visual light field' is defined even in the 'empty space' between objects. In that sense the light field is akin to visual space considered as a 'container'. The visual light field at any given point can be measured in psychophysical experiments through the introduction of a suitable 'gauge object' at that position and letting the observer adjust the appearance of that gauge object (eg through suitable computer rendering) so as to produce a 'visual fit' into the scene. The parameters of the rendering will then be considered as the measurement result. We introduced white spheres as gauge objects at various locations in stereoscopically presented photographic scenes. We measured the direction ('direction of the light'), diffuseness ('quality of the light' as used by photographers and interior decorators), and intensity of the light field. We used three very different scenes, with very different physical light fields. The images were geometrically and photometrically calibrated, so we were in a position to correlate the observations with the physical 'ground truth'. We report that human observers are quite sensitive to various parameters of the physical light field and generally arrive at close to veridical settings, although a number of comparatively minor systematic deviations from veridicality can be noted. We conclude that the visual light field is an entity whose existence is at least as well defined as that of visual space, despite the fact that the visual light field hardly appears as prominently in vision science as it does in the visual arts.     

Contribution of somatosensory information to perception of the visual vertical with body tilt and rotating visual field

This study was designed to explore the role of somatosensory information from the trunk in the perception of the visual vertical. Twelve normal subjects and 1 subject with no somatosensory function below the neck attempted to set a line to the true vertical in the sitting and lying positions, first with a static visual background and then with rotation of the background about the line of sight. The absence of somatosensory information did not affect accuracy when the subjects were in the upright position. When lying horizontally, all control subjects experienced a substantial perceived tilt of the vertical in the direction of body tilt (the A effect), but, in contrast, the subject lacking somatosensory function exhibited a small but consistent apparent tilt of the vertical in the opposite direction (the E effect). This finding is discussed in relation to two competing hypotheses regarding the mechanisms subserving apparent displacement of the subjective vertical in tilted subjects.     

Orientation sensitivity in the peripheral visual field

Orientation sensitivity in the peripheral visual field has been tested in two tasks: (a) setting horizontal the orientation of a grating at various retinal eccentricities, and (b) matching the orientation of a peripherally viewed grating as close as possible to an oblique reference viewed foveally. Both performances fall off with increasing retinal eccentricity. Magnification of the stimulus optimizes peripheral performance. Peripheral performance, optimized by magnification, varies with retinal eccentricity. It approaches, but does not reach, the foveal value (tested by the same method) at 10 deg of eccentricity, and is much lower at 20 and 30 deg of eccentricity.     

The constancy of the orientation of the visual field

Evidence is presented that the perceived immobility of the environment during tilting of the head from side to side results from a compensating process. This compensating process operates well only when peripheral vision is present. An objectively stationary environment was, for instance, not perceived as immobile during head tilting when vision was confined to the macular region of the retina. The compensating process could be rapidly altered by exposure to environmental tilting during and dependent on head tilting. Such adaptation had the result that some environmental tilting that normally is perceived led to apparent immobility.     

Asymmetry of the effective visual field in reading

In three experiments, subjects’ eye movements were recorded as they read from a computer-controlled CRT. The amount of information available to the left and right of the fixation point was varied in order to determine the characteristics of the effective visual field in reading. Experiments 1 and 2 demonstrated that readers do not obtain useful information during a fixation more than 3 or 4 letters to the left of their fixation point. The results of Experiment 3 indicated that the effective visual field does not extend any further to the left than the beginning of the word currently fixated, independent of the number of letters available to the left of fixation. When combined with the results of other research on the perceptual span in reading, the results of these experiments indicate that the effective visual field extends from the beginning of the currently fixated word (but no further than 4 characters to the left of fixation) up to about 15 characters to the right of fixation.