Biomedical subjects

M S Banks

Publications and source records attributed to M S Banks.

At least 19 recordsLinked to original sources

PubMed1999

Horizontal and vertical disparity, eye position, and stereoscopic slant perception.

The slant of a stereoscopically defined surface cannot be determined solely from horizontal disparities or from derived quantities such as horizontal size ratio (HSR). There are four other signals that, in combination with horizontal disparity, could in principle allow an unambiguous estimate of slant: the vergence and version of the eyes, the vertical size ratio (VSR), and the horizontal gradient of VSR. Another useful signal is provided by perspective slant cues. The determination of perceived slant can be modeled as a weighted combination of three estimates based on those signals: a perspective estimate, a stereoscopic estimate based on HSR and VSR, and a stereoscopic estimate based on HSR and sensed eye position. In a series of experiments, we examined human observers' use of the two stereoscopic means of estimation. Perspective cues were rendered uninformative. We found that VSR and sensed eye position are both used to interpret the measured horizontal disparities. When the two are placed in conflict, the visual system usually gives more weight to VSR. However, when VSR is made difficult to measure by using short stimuli or stimuli composed of vertical lines, the visual system relies on sensed eye position. A model in which the observer's slant estimate is a weighted average of the slant estimate based on HSR and VSR and the one based on HSR and eye position accounted well for the data. The weights varied across viewing conditions because the informativeness of the signals they employ vary from one situation to another.

Cues↗

PubMed1998

Extra-retinal and perspective cues cause the small range of the induced effect.

With a horizontal magnifier before one eye, a frontoparallel surface appears rotated about a vertical axis (geometric effect). With a vertical magnifier, apparent rotation is opposite in direction (induced effect); to restore appearance of frontoparallelism, the surface must be rotated away from the magnified eye. The induced effect is interesting because it was thought until recently that vertical disparities do not play an important role in surface perception. As with the geometric effect, the required rotation for the induced effect increases linearly to approximately equal to 4% magnification; unlike the geometric effect, it plateaus at approximately 8%. Current theory explains the linear portion: vertical size ratios (VSRs) are used to compensate for changes in horizontal size ratios (HSRs) that accompany eccentric gaze, so changes in VSR cause changes in perceived slant. The theory does not explain the plateau. We demonstrate that it results from differing slant estimates obtained by use of various retinal and extra-retinal signals. When perspective cues to slant are minimized or sensed eye position is consistent with VSR, the induced and geometric effects have similar magnitudes even at large magnifications.

Cues↗

PubMed1998

Perceived head-centric speed is affected by both extra-retinal and retinal errors.

When we make a smooth eye movement to track a moving object, the visual system must take the eye's movement into account in order to estimate the object's velocity relative to the head. This can be done by using extra-retinal signals to estimate eye velocity and then subtracting expected from observed retinal motion. Two familiar illusions of perceived velocity--the Filehne illusion and Aubert-Fleischl phenomenon--are thought to be the consequence of the extra-retinal signal underestimating eye velocity. These explanations assume that retinal motion is encoded accurately, which is questionable because perceived retinal speed is strongly affected by several stimulus properties. We develop and test a model of head-centric velocity perception that incorporates errors in estimating eye velocity and in retinal-motion sensing. The model predicts that the magnitude and direction of the Filehne illusion and Aubert-Fleischl phenomenon depend on spatial frequency and this prediction is confirmed experimentally.

Head↗

PubMed1998

Depth information and perceived self-motion during simulated gaze rotations.

When presented with random-dot displays with little depth information, observers cannot determine their direction of self-motion accurately in the presence of rotational flow without appropriate extra-retinal information (Royden CS et al. Vis Res 1994;34:3197-214.). On theoretical grounds, one might expect improved performance when depth information is added to the display (van den Berg AV and Brenner E. Nature 1994;371:700-2). We examined this possibility by having observers indicate perceived self-motion paths when the amount of depth information was varied. When stereoscopic cues and a variety of monocular depth cues were added, observers still misperceived the depicted self-motion when the rotational flow in the display was not accompanied by an appropriate extra-retinal, eye-velocity signal. Specifically, they perceived curved self-motion paths with the curvature in the direction of the simulated eye rotation. The distance to the response marker was crucial to the objective measurement of this misperception. When the marker distance was small, the observers' settings were reasonably accurate despite the misperception of the depicted self-motion. When the marker distance was large, the settings exhibited the errors reported previously by Royden CS et al. Vis Res 1994;34-3197-3214. The path judgement errors observers make during simulated gaze rotations appear to be the result of misattributing path-independent rotation to self-motion along a circular path with path-dependent rotation. An analysis of the information an observer could use to avoid such errors reveals that the addition of depth information is of little use.

Cues↗

PubMed1998

Optical, receptoral, and retinal constraints on foveal and peripheral vision in the human neonate.

We examined the properties of the foveal, parafoveal, and near peripheral cone lattice in human neonates. To estimate the ability of these lattices to transmit the information used in contrast sensitivity and visual acuity tasks, we constructed ideal-observer models with the optics and photoreceptors of the neonatal eye at retinal eccentricities of 0, 5, and 10 degrees. For ideal-observer models limited by photon noise, the eye's optics, and cone properties, contrast sensitivity was higher in the parafovea and near periphery than in the fovea. However, receptor pooling probably occurs in the neonate's parafovea and near periphery as it does in mature eyes. When we add a receptor-pooling stage to the models of the parafovea and near periphery, ideal acuity is similar in the fovea, parafovea, and near periphery. Comparisons of ideal and real sensitivity indicate that optical and receptoral immaturities impose a significant constraint on neonatal contrast sensitivity and acuity, but that immaturities in later processing stages must also limit visual performance.

Contrast Sensitivity↗

PubMed1998

Visual self-motion perception during head turns.

Extra-retinal information is critical in the interpretation of visual input during self-motion. Turning our eyes and head to track objects displaces the retinal image but does not affect our ability to navigate because we use extra-retinal information to compensate for these displacements. We showed observers animated displays depicting their forward motion through a scene. They perceived the simulated self-motion accurately while smoothly shifting the gaze by turning the head, but not when the same gaze shift was simulated in the display; this indicates that the visual system also uses extra-retinal information during head turns. Additional experiments compared self-motion judgments during active and passive head turns, passive rotations of the body and rotations of the body with head fixed in space. We found that accurate perception during active head turns is mediated by contributions from three extra-retinal cues: vestibular canal stimulation, neck proprioception and an efference copy of the motor command to turn the head.

Cues↗

PubMed1997

The computation of binocular visual direction: a re-examination of Mansfield and Legge (1996)

Mansfield and Legge (1996) reported recently that a target's perceived binocular direction is dependent on the ratio of contrasts presented to the two eyes. Although their main conclusion concerned the dependence of perceived direction on interocular contrast, they also argued that the change in perceived direction is due to a shift in the position of the cyclopean eye and that the relative directions of binocular targets are unaffected by eye position. We take issue with both of these arguments. With regard to the former, their task was an alignment task, not an egocenter task, so it did not provide information relevant to the position of the cyclopean eye. Indeed, their data can be explained by the conventional theory of binocular visual directions with a fixed cyclopean eye (e.g., Hering, 1879; Ono, 1981) once a simple, but important modification is added. With regard to their conclusion concerning eye position, we show that the vergence of the eyes has a clear and systematic effect on perceived relative directions in the setup used by Mansfield and Legge.

Contrast Sensitivity↗

PubMed1996

Mechanisms of heading perception in primate visual cortex.

When we move forward while walking or driving, what we see appears to expand. The center or focus of this expansion tells us our direction of self-motion, or heading, as long as our eyes are still. However, if our eyes move, as when tracking a nearby object on the ground, the retinal image is disrupted and the focus is shifted away from the heading. Neurons in primate dorso-medial superior temporal area responded selectively to an expansion focus in a certain part of the visual field, and this selective region shifted during tracking eye movements in a way that compensated for the retinal focus shift. Therefore, these neurons account for the effect of eye movements on what we see as we travel forward through the world.

Animals↗

PubMed1996

Retinal illuminance and contrast sensitivity in human infants.

Several investigators have related infants' low contrast sensitivity to immaturities in the optics and receptor lattice of the immature eye. A critical element in the modeling is how much the lower photon catch of the immature retina reduces sensitivity; the assumptions vary from square-root to Weber's law and lead to very different modeling outcomes. We measured the relationship between retinal illuminance and contrast sensitivity at different spatial frequencies. The sweep visual-evoked potential was used to measure thresholds in 2- and 3-month olds and adults over a 2.5-log-unit range of illuminances. The contrast threshold vs illuminance functions were fit by power functions. The best-fitting exponents for adults were about -0.5 at higher spatial frequencies (consistent with square-root law) and lower at lower frequencies. The best-fitting exponents for 2- and 3-month olds were -0.2 to -0.35 which indicates that threshold is less affected by changes in illuminance than is the case in adults. These results suggest that none of the models relating optical and receptoral immaturities to infants' spatial vision has assumed an appropriate relationship between lower photon catch and contrast sensitivity. Once the models are modified to incorporate the relationship obtained in the present experiment, the predictions fall well short of explaining 2-month olds' low contrast sensitivity.

Adult↗

PubMed1996

Ideal observer for heading judgments.

Several aspects of the viewing situation affect the ability to determine heading from optical flow. These include the amount of depth variation and number of texture elements in the scene, the location and amount of the visual field stimulated, and the position of the focus of expansion within the stimulus. Without a quantification of the discrimination information provided by the stimuli presented to the observer, it is impossible to determine how much of an observed change in performance reflects the properties of neural mechanisms and strategies employed by the observer. To enable a better quantification, we developed an ideal observer for the discrimination of heading from random-dot flow fields. Internal noises of the ideal observer were set by the results of single-dot velocity discrimination experiments. We compared human and ideal observer performance in discriminating headings with different patterns of flow (e.g. radial vs laminar) presented on different parts of the retina. Efficiency--the ratio of ideal and human thresholds--was fairly constant for the various flow patterns and retinal eccentricities. This outcome indicates that most of the variation in human observers' ability to estimate heading from the flow patterns and retinal loci considered here is due to changes in the discrimination information provided by the stimulus after measurement by the visual system. In the discussion, we show how the ideal observer can be used to quantify the spatial distribution of heading discrimination information for any observer translation through any scene represented by dots.

Depth Perception↗

PubMed1996

Estimating heading during real and simulated eye movements.

The ability to judge heading during tracking eye movements has recently been examined by several investigators. To assess the use of retinal-image and extra-retinal information in this task, the previous work has compared heading judgments with executed as opposed to simulated eye movements. For eye movement velocities greater than 1 deg/sec, observers seem to require the eye-velocity information provided by extra-retinal signals that accompany tracking eye movements. When those signals are not provided, such as with simulated eye movements, observers perceive their self-motion as curvilinear translation rather than the linear translation plus eye rotation being presented. The interpretation of the previous results is complicated, however, by the fact that the simulated eye movement condition may have created a conflict between two possible estimates of the heading: one based on extra-retinal solutions and the other based on retina-image solutions. In four experiments, we minimized this potential conflict by having observers judge heading in the presence of rotations consisting of mixtures of executed and simulated eye movements. The results showed that the heading is estimated more accurately when rotational flow is created by executed eye movements alone. In addition, the magnitude of errors in heading estimates is essentially proportional to the amount of rotational flow created by a simulated eye rotation (independent of the total magnitude of the rotational flow). The fact that error magnitude is proportional to the amount of simulated rotation suggests that the visual system attributes rotational flow unaccompanied by an eye movement to a displacement of the direction of translation in the direction of the simulated eye rotation.

Cues↗

PubMed1996

Gravitational acceleration as a cue for absolute size and distance?

When an object's motion is influenced by gravity, as in the rise and fall of a thrown ball, the vertical component of acceleration is roughly constant at 9.8 m/sec2. In principle, an observer could use this information to estimate the absolute size and distance of the object (Saxberg, 1987a; Watson, Banks, von Hofsten, & Royden, 1992). In five experiments, we examined people's ability to utilize the size and distance information provided by gravitational acceleration. Observers viewed computer simulations of an object rising and falling on a trajectory aligned with the gravitational vector. The simulated objects were balls of different diameters presented across a wide range of simulated distances. Observers were asked to identify the ball that was presented and to estimate its distance. The results showed that observers were much more sensitive to average velocity than to the gravitational acceleration pattern. Likewise, verticality of the motion and visibility of the trajectory's apex had negligible effects on the accuracy of size and distance judgments.

Acceleration↗

PubMed1994

Estimating heading during eye movements.

In eight experiments, we examined the ability to judge heading during tracking eye movements. To assess the use of retinal-image and extra-retinal information in this task, we compared heading judgments with executed as opposed to simulated eye movements. In general, judgments were much more accurate during executed eye movements. Observers in the simulated eye movement condition misperceived their self-motion as curvilinear translation rather than the linear translation plus eye rotation that was simulated. There were some experimental conditions in which observers could judge heading reasonably accurately during simulated eye movements; these included conditions in which eye movement velocities were 1 deg/sec or less and conditions which made available a horizon cue that exists for locomotion parallel to a ground plane with a visible horizon. Overall, our results imply that extra-retinal, eye-velocity signals are used in determining heading under many, perhaps most, viewing conditions.

Algorithms↗

PubMed1993

Does chromatic sensitivity develop more slowly than luminance sensitivity?

Chromatic sensitivity is very low in humans during the first few months of life. We examined whether low chromatic sensitivity reflects a deficiency among chromatic mechanisms or whether it is simply a manifestation of poor visual sensitivity in general. The sweep VEP was used to measure contrast sensitivity to gratings varying in the mixture of red and green components. For infants from 2 to 8 weeks of age, sensitivity to all mixtures was lower than color-normal adults' sensitivity, but infant and adult ratios of luminance/chromatic sensitivity were similar. This finding is consistent with the hypothesis that infants have functional MWS and LWS cones and the requisite post-receptor chromatic mechanisms to compare their signals.

Age Factors↗

PubMed1993

Perceiving heading with different retinal regions and types of optic flow.

We examined the ability to use optic flow to judge heading when different parts of the retina are stimulated and when the specified heading is in different directions relative to the display. To do so, we manipulated retinal eccentricity (the angle between the fovea and the center of the stimulus) and heading eccentricity (the angle between the specified heading and the center of the stimulus) independently. Observers viewed two sequences of moving dots that simulated translation through a random cloud of dots. They reported whether the direction of translation--the heading--in the second sequence was to the left or right of the direction in the first sequence. The results revealed a large and consistent effect of heading eccentricity: Judgments were much more accurate with radial flow fields (small heading eccentricities) than with lamellar fields (large heading eccentricities), regardless of the part of the retina being stimulated. The results also revealed a smaller and less consistent effect of retinal eccentricity: With radial flow (small heading eccentricities), judgments were more accurate when the stimulus was presented near the fovea. The variation of heading thresholds from radial to lamellar flow fields is predicted by a simple model of two-dimensional motion discrimination. The fact that the predictions are accurate implies that the human visual system is equally efficient at processing radial and lamellar flow fields. In addition, efficiency is reasonably constant no matter what part of the retina is being stimulated.

Depth Perception↗

PubMed1992

The perception of heading during eye movements.

When a person walks through a rigid environment while holding eyes and head fixed, the pattern of retinal motion flows radially away from a point, the focus of expansion (Fig. 1a). Under such conditions of translation, heading corresponds to the focus of expansion and people identify it readily. But when making an eye/head movement to track an object off to the side, retinal motion is no longer radial (Fig. 1b). Heading perception in such situations has been modelled in two ways. Extra-retinal models monitor the velocity of rotational movements through proprioceptive or efference information from the extraocular and neck muscles and use that information to discount rotation effects. Retinal-image models determine (and eliminate) rotational components from the retinal image alone. These models have been tested by measuring heading perception under two conditions. First, observers judged heading while tracking a point on a simulated ground plane. Second, they fixated a stationary point and the flow field simulated the effects of a tracking eye movement. Extra-retinal models predict poorer performance in the simulated condition because the eyes do not move. Retinal-image models predict no difference in performance because the two conditions produce identical patterns of retinal motion. Warren and Hannon observed similar performance and concluded that people do not require extra-retinal information to judge heading with eye/head movements present, but they used extremely slow tracking eye movements of 0.2-1.2 deg s-1; a moving observer frequently tracks objects at much higher rates (L. Stark, personal communication). Here we examine heading judgements at higher, more typical eye movement velocities and find that people require extra-retinal information about eye position to perceive heading accurately under many viewing conditions.

Eye Movements↗

PubMed1992

Temporal contrast sensitivity in human infants.

Temporal contrast sensitivity was measured in 1.5- and 3-month-old infants using the FPL procedure. Stimuli were 0.1 c/deg counterphase-flickering sinewave gratings. Temporal rates ranged from 1 to 20 Hz. Because the spatial sinewave underwent phase shifts of 180 degrees, the target could not be seen unless the observer was able to resolve it temporally. Adults were tested with the same temporal stimuli using a 2-alternative forced-choice procedure and a spatial frequency of 0.5 c/deg. Adult temporal CSFs were bandpass with peak sensitivity at 10 Hz. Infant temporal CSFs were lowpass at 1.5 months and bandpass at 3 months. The infants' contrast sensitivity was over a log-unit lower than adults'. Unlike spatial CSFs, infant sensitivity was closest to adult sensitivity at the highest flicker rate.

Adult↗

PubMed1992

The effects of luminance on FPL and VEP acuity in human infants.

Grating acuity was measured in 16-week-old human infants. Three measurement techniques were used: forced-choice preferential-looking (FPL), and two visual-evoked-potential (VEP) techniques. The stimuli were counterphase flickering sinewave gratings with a space-average luminance of -1.0 or 2.0 log cd/m2. Slightly different luminance-dependent changes occur between FPL and VEP acuities, suggesting that some factor influences the two methods differently as stimulus luminance varies. A comparison between FPL acuities and VEP acuities within infants suggests a quantitative relationship between techniques. Infant's acuity for sinewave gratings with a space-average luminance of -2.0, -1.0, 0.0, 1.0 and 2.0 log cd/m2 was also measured using a single VEP paradigm. The results are compared to the same measurements in adults and to infant and adult ideal observers. VEP acuity in this group of infants improves by about 0.5 log units between -2.0 and 0.0 log cd/m2 and remains asymptotic between 0.0 and 2.0 log cd/m2. This result suggests that luminance-dependent changes in infant acuity cannot be fully accounted for by immaturities in the optics and photoreceptor spacing and efficiency.

Evoked Potentials, Visual↗