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B Bridgeman

Publications and source records attributed to B Bridgeman.

At least 19 recordsLinked to original sources
PubMed2000

Processing spatial information in the sensorimotor branch of the visual system.

We distinguish two representations of visual space: a cognitive representation drives perception, and a sensorimotor representation controls visually guided behavior. Spatial values in the two representations are separated with the Roelofs effect: a target within an off-center frame appears biased in a location opposite the direction of the frame. The effect appears for a verbal measure (cognitive) but not for a jab at the target (sensorimotor). A 2-s response delay induces a Roelofs effect in the motor measure, showing the limit of motor memory. Motor error is not correlated with reaction time. Subjects could strike one of two identical targets, a process involving choice, without intrusion of a Roelofs effect, showing that the sensorimotor system can use its own coordinates even when a cognitive choice initiates the motor processing.

Cognition↗
PubMed1999

Neither strong nor weak space constancy is coded in striate cortex.

Space constancy (the perception that the world remains stable despite eye movements) might be mediated by receptive fields with constant locations in the world rather than constant locations on the retina. In a strong form the hypothesis, receptive fields of single neurons would compensate for all eye movements, whereas in a weak form they would compensate only for the small movements of fixation that occur without retargeting. Early receptive field mapping confounded world-centered and retina-centered organizations by fixing the retina relative to the world. This paper links the strong and weak forms of constancy by relating previously isolated data, and illustrates the issues with a previously unpublished figure showing that striate receptive field have constant retinal locations. The first tests of space constancy in striate cortex contradicted the strong hypothesis; recent tests contradict the weak hypothesis, also. The results are consistent with modern theories of space constancy, differentiating between motor-oriented and perceptual functions of vision, and differentiating between constancy during pursuit and constancy across saccades.

Animals↗
PubMed1998

A spatially oriented decision does not induce consciousness in a motor task.

Visual information follows at least two branches in the human nervous system, following a common input stage: a cognitive "what" branch governs perception and experience, while a sensorimotor "how" branch handles visually guided behavior though its outputs are unconscious. The sensorimotor system is probed with an isomorphic task, requiring a 1:1 relationship between target position and motor response. The cognitive system, in contrast, is probed with a forced qualitative decision, expressed verbally, about the location of a target. Normally, the cognitive system is influenced by context-induced illusions of visual direction, while the sensorimotor system is not. Here, we inquire whether the process of making a spatially based decision is critical in forcing subjects to use the information in the cognitive system for spatial tasks. Subjects hear a tone that determines whether they jab an "X" or an "O" with the forefinger. Despite making a decision about which target to contact, the jab is not influenced by the position of a surrounding frame, indicating that choice can be handled within the context-insensitive sensorimotor system.

Adult↗
PubMed1998

Immediate post-saccadic information mediates space constancy.

We recently demonstrated that the perceived stability of a visual target that is displaced during a saccade critically depends on whether the target is present immediately when the saccade ends; blanking a target during and just after a saccade makes its intra-saccadic displacement more visible (Deubel et al. Vis Res 1996;36:985-996). Here, we investigate the interaction of visual context and blanking. Subjects saw a saccade target and an equal-sized distractor. During a saccade one or the other was displaced left or right. At the same time, one of the objects could be blanked briefly. Subjects reported whether the target or the distractor had jumped. The object that was blanked was more often seen as jumping (Experiment 1), regardless of which object really jumped, implying that continuously visible objects are preferentially perceived as stable. When both objects were blanked, longer blanking led to better accuracy at identifying which had jumped during a saccade. When one object was jumped and the other, stationary object was blanked (Experiment 2), the blanked object was mistakenly seen as jumping until the jump covered 50% or more of the saccade amplitude. In Experiment 3 a large continuously present texture underwent an undetected jump during a saccade, biasing judgments of simultaneous jumps of a blanked target. The results demonstrate that space constancy in normal situations is dominated by the assumption that a continuously present pattern is stable--this pattern becomes the spatial reference for the post-saccadic recalibration of perceptual space.

Adult↗
PubMed1998

Dual adaptation and adaptive generalization of the human vestibulo-ocular reflex.

In two experiments, we examined the possibility that the human vestibulo-ocular reflex (VOR) is subject to dual adaptation (the ability to adapt to a sensory rearrangement more rapidly and/or more completely after repeated experience with it) and adaptive generalization (the ability to adapt more readily to a novel sensory rearrangement as a result of prior dual adaptation training). In Experiment 1, the subjects actively turned the head during alternating exposure to a visual-vestibular rearrangement (target/head gain = 0.5) and the normal situation (target/head gain = 0.0). These conditions produced both adaptation and dual adaptation of the VOR but no evidence of adaptive generalization when tested with a target/head gain of 1.0. Experiment 2, in which exposure to the 0.5 gain entailed externally controlled (i.e., passive) whole body rotation, resulted in VOR adaptation but no dual adaptation. As in Experiment 1, no evidence of adaptive generalization was found.

Adaptation, Physiological↗
PubMed1997

High refresh rate and oculomotor adaptation facilitate reading from video displays.

Reading from a video display terminal (VDT) was tested at screen refresh rates of 500 Hz and 60 Hz. Reading was initially 8 words/min (3.05%) faster at 500 Hz. A hypothesis that reading rate on VDTs is limited by stimulus availability accounts for the difference. When the eye reaches a new fixation position, it 'parks' until a sample of text appears at the fovea. Then processing resumes in the normal way. This idea, combined with the 500-Hz reading data, can predict reading rate at any refresh rate, and is quantitatively confirmed by the reading rate at 60 Hz. The difference in reading rates disappeared for the second half of the text, as a result of differences between frequencies of eye movements in the two refresh conditions. From the first half to the second, subjects at 60 Hz made more large forward saccades and fewer small reverse saccades. Both changes make sampling of the text more sparse, compensating for the dead time between samples. Subjects were unaware of refresh conditions, differences in their reading rates, and types of eye movements they generated. Reading from a continuously illuminated active-matrix display is slightly faster than from a comparable VDT.

Adaptation, Ocular↗
PubMed1997

Interaction of cognitive and sensorimotor maps of visual space.

Studies of saccadic suppression and induced motion have suggested separate representations of visual space for perception and visually guided behavior. Because these methods required stimulus motion, subjects might have confounded motion and position. We separated cognitive and sensorimotor maps without motion of target, background, or eye, with an "induced Roelofs effects": a target inside an off-center frame appears biased opposite the direction of the frame. A frame displayed to the left of a subject's center line, for example, will make a target inside the frame appear farther to the right than its actual position. The effect always influences perception, but in half of our subjects it did not influence pointing. Cognitive and sensorimotor maps interacted when the motor response was delayed; all subjects now showed a Roelofs effect for pointing, suggesting that the motor system was being fed from the biased cognitive map. A second experiment showed similar results when subjects made an open-ended cognitive response instead of a five-alternative forced choice. Experiment 3 showed that the results were not due to shifts in subjects' perception of the felt straight-ahead position. In Experiment 4, subjects pointed to the target and judged its location on the same trail. Both measures showed a Roelofs effect, indicating that each trial was treated as a single event and that the cognitive representation was accessed to localize this event in both response modes.

Cognition↗
PubMed1996

Postsaccadic target blanking prevents saccadic suppression of image displacement.

Displacement of a visual target during a saccadic eye movement is normally detected only at a high threshold, implying that high-quality information about target position is not stored in the nervous system across the saccade. We show that blanking the target for 50-300 msec after a saccade restores sensitivity to the displacement. With blanking, subjects reliably detect displacements as small as 0.33 deg across 6 deg eye movements, with correspondingly steep psychophysical functions. Performance with blanking in a fixation control is inferior, evidence for a saccadic enhancement of sensitivity to image displacement. If blanking is delayed so that the target is visible immediately after the saccade in its displaced position, performance declines to non-blanking levels. Blanking the target before the saccade, and restoring it during the saccade, yields a similar but weaker effect. We interpret these results with a model in which the visual system searches for the postsaccadic goal target within a restricted spatiotemporal window. If it is not found, the assumption of stationarity of the world is broken and the system makes use of other information such as extraretinal signals for calibrating location.

Adult↗
PubMed1995

Saccadic suppression relies on luminance information.

To determine whether saccadic suppression of image displacement uses information from luminance channels, we measured spatial displacement detection thresholds with equiluminant and non-equiluminant targets during saccades. We compared these saccadic thresholds with displacement thresholds measured during fixation by making ratios of saccadic thresholds to fixation thresholds. Ratios were lower in the equiluminant condition than in the non-equiluminant. This surprising result indicates that detection of equiluminant target displacements during saccades was better than detection of nonequiluminant targets, compared with the detection abilities during fixation. Thus, saccadic suppression of image displacement, which should increase displacement thresholds during saccades over fixation thresholds, was more effective with nonequiluminant targets. Because of target flicker, displacement thresholds were anisotropic in the nonequiluminant condition; thresholds were greater when target and eye moved in the same direction than when they moved in opposite directions, consistent with earlier results. These two effects (flicker-induced anisotropy and greater suppression in nonequiluminance) canceled when the eye moved opposite the displacement, yielding equal thresholds and summed when eye and target moved in the same direction, yielding large threshold differences. We conclude that saccadic suppression of image displacement uses mechanisms sensitive to luminance contrast.

Anisotropy↗
PubMed1995

Visual stability with goal-directed eye and arm movements toward a target displaced during saccadic suppression.

This experiment tested whether the perceived stability of the environment is altered when there is a combination of eye and visually open-loop hand movements toward a target displaced during the eye movements, i.e., during saccadic suppression. Visual-target eccentricity randomly decreased or increased during eye movements and subjects reported whether they perceived a target displacement or not, and if so, the direction of the displacement. Three experimental conditions, involving different combinations of eye and arm movements, were tested: (a) eye movements only; (b) simultaneous eye and rapid arm movements toward the target; and (c) simultaneous eye and arm movements with a restraint blocking the arm as soon as the hand left the starting position. The perceptual threshold of target displacements resulting in an increased target eccentricity was greater when subjects combined eye and arm movements toward the target object, specially for the no-restraint condition. Subjects corrected most of their arm trajectory toward the displaced target despite the short movement times (average MT = 189 ms). After the movements, the null error feedback of the hand's final position presumably overlapped the retino-oculomotor signal error and could be responsible for the deficient perception of target displacements. Thus, subjects interpreted the terminal hand positions as being within the range of the endpoint variability associated with the production of rapid arm movements rather than as a change of the environment. These results suggest that a natural strategy adopted for processing spatial information, especially in a competing situation, could favour a constancy tendency avoiding systematic perception of a change of environment for any noise or variability at the central or peripheral levels.

Adult↗
PubMed1995

Fourth Purkinje image signals reveal eye-lens deviations and retinal image distortions during saccades.

Saccadic eye movements of various sizes and directions were registered simultaneously with the scleral search coil and a fifth-generation Dual Purkinje image eyetracker. Comparison of the search coil and the Purkinje image tracker records reveal considerable dynamic deviations during and immediately after the saccade, which we ascribe to the movements of the eye lens relative to the optical axis of the eye. Due to the increased stiffness of the tissues these deviations are smaller in older subjects. Also, they are larger at near accommodation. The size of the retinal image displacement which results from the lens movement proper can be as large as 0.5 deg, which may not be negligible in a number of visual tasks.

Accommodation, Ocular↗
PubMed1995

Perceptual consequences of ocular lens overshoot during saccadic eye movements.

In a previous paper we compared eye globe records of saccadic eye movements (recorded with a scleral eye coil) with lens reflection records of the same eye movements (recorded with a dual-Purkinje-image eyetracker); we found evidence for considerable dynamic deviations between the two during and immediately after saccades. We ascribed these deviations to the movements of the eye's lens relative to the optical axis of the eye. This paper quantifies a predicted psychophysical effect of lens displacements during and after saccades. Two small targets, one above the other, were flashed for 2 msec in total darkness, the bottom one exactly at the end of the saccade, the top one 30 msec later. The first target appears deviated horizontally relative to the other, in a direction opposite to the saccade. Magnitude of the relative mislocalization can be up to 0.03 deg for each degree of saccadic eye movement. The result shows that the position of the visual image on the retina is affected both by position of the globe and by deviations of the lens from its normal location.

Adult↗
PubMed1994

Conflict between aftereffects of retinal sweep and looming motion.

Observers looked monocularly into a tunnel, with gratings on the left and right sides drifting toward the head. An exposure period was followed by a test with fixed gratings. With fixation points, left and right retinal fields could be stimulated selectively. When exposure and test were on the same retinal fields, but fixation was on opposite sides of the tunnel during exposure and test periods, aftereffects of retinal sweep and of perceived looming were in opposite directions. The two effects tended to cancel, yielding no perceived aftereffect. When they did occur, aftereffects in the retinal and the looming directions were equally likely. Cancellation was significantly more likely in the experimental conditions than in the control, when fixation always remained on the same side. When areas of retinal stimulation in the exposure and test periods did not overlap, cancellation was less frequent and aftereffects of looming were more frequent. Results were not significantly different for left and right visual fields, indicating that cortical vs. subcortical OKN pathways do not influence the illusion. Vection resulted for 16 of 20 observers under one or another of our conditions.

Adult↗
PubMed1993

Spatial context affects the Poggendorff illusion.

The Poggendorff illusion has often been explained as purely an interaction between the parallels and the transversals. The present study demonstrates that additional spatial context exerts an influence on this illusion. In Experiment 1, we examined the effects of a surrounding tilted frame (complete and degraded versions) on collinearity adjustments in the upright and rotated Poggendorff figures. The frame's orientation was always oblique. Relative to the no-frame condition, frames decreased error in collinearity adjustments in the upright Poggendorff figure, and increased error in the rotated Poggendorff figure. In Experiment 2, a circumscribing circle did not cause an orientation-inhibition effect (Ebenholtz & Utrie, 1982, 1983), suggesting that the effect of the frame on the Poggendorff illusion may not be closely related to the rod-and-frame effect. In Experiment 3, orientation of a central texture modulated the magnitude of the illusion. The results do not serve to explain the mechanisms behind the Poggendorff illusion, but they do demonstrate the importance of visual reference frames in understanding perceived misalignment.

Adult↗
PubMed1993

Alternating prism exposure causes dual adaptation and generalization to a novel displacement.

In two experiments, we examined the hypothesis that repeatedly adapting and readapting to two mutually conflicting sensory environments fosters the development of a separate adaptation to each situation (dual adaptation) as well as an increased ability to adapt to a novel displacement (adaptive generalization). In the preliminary study, subjects alternated between adapting their visuomotor coordination to 30-diopter prismatic displacement and readapting to normal vision. Dual adaptation was observed by the end of 10 alternation cycles. However, an unconfounded test of adaptive generalization was prevented by an unexpected prism-adaptive shift in preexposure baselines for the dual-adapted subjects. In the primary experiment, the subjects adapted and readapted to opposite 15-diopter displacements for a total of 12 cycles. Both dual adaptation and adaptive generalization to a 30-diopter displacement were obtained. These findings may be understood in terms of serial reversal learning and "learning to learn."

Adaptation, Psychological↗
PubMed1991

Flicker distorts visual space constancy.

Effects of flicker on space perception were measured by displacing a flickering target during saccadic eye movements. A small target was flickered at 33, 66, 130 or 260 Hz. Using a 2-interval forced-choice design, sensitivity to the displacement was about twice as great when the target was moved in the direction opposite the eye movement as when it was moved in the same direction. This would be expected from a partial breakdown of space constancy--the world should seem to jump in the direction opposite an eye movement. Even if a suppression of displacement detection during saccades prevents this jump from being perceived; it should be easier to detect a target displacement in the direction opposite the eye movement than in the same direction: when movement is opposite, the imposed displacement adds to the illusory displacement, making detection easier. Displacements were more easily detected at lower flicker rates. Results imply that both masking and extraretinal signals are important in suppressing the detectability of target displacements during saccades, and that flicker on video display terminals may distort space perception.

Humans↗
PubMed1991

Ocular proprioception and efference copy in registering visual direction.

We measured the roles of eye muscle proprioception ("inflow") and efference copy ("outflow") in registering eye position. During monocular fixation, pressing on the side of an occluded eye results in a passive rotation, changing the proprioception without affecting oculomotor efference. As we have shown previously, a constant press on the side of the viewing eye induces active resistance to rotation, changing efference because oculomotor innervation compensates for the eyepress; the viewing eye's fixation remains constant. Using these two types of eyepress, both perceived target deviations and pointing biases in an unstructured visual field were measured in 8 subjects under efference copy, proprioception and control (no eyepress) conditions. Eye deviation was measured photoelectrically. Physiological gains of efference copy and proprioception was about 5/8 and 1/4 respectively. There was no statistically significant difference between perceptual judgement and open-loop pointing. The sum of gains of efference copy and proprioception, about 7/8, indicates incomplete registration of eye eccentricity in an unstructured field, and quantitatively accounts for several previously unexplained results in the literature.

Adult↗