Growing older does not always mean moving slower: examining aging and the saccadic motor system

Although humans typically move more slowly as they age, one exception may be the saccadic motor system. To fully determine whether the execution of saccades is affected by age, the authors examined detailed kinematics of vertical and horizontal saccades across a range of saccadic amplitudes (4 degrees, 8 degrees, and 12 degrees). Ten younger and 20 older adults participated in each experiment. Whereas in the 1st experiment, the authors assessed volitionally generated saccades, in the 2nd experiment, they evaluated reflexively generated saccades. The results of those experiments showed that the saccadic motor system is relatively impervious to the effects of aging; in fact, the differences between vertical and horizontal saccades were more evident than were differences between saccades produced by younger and older adults. The authors discuss possible reasons for that relative resistance to aging.     

Effects of illusory stripes on the Helmholtz illusion

This study examined the Helmholtz illusion by using "illusory stripes." A square patch is perceived as wider when vertical lines are drawn on it and is perceived as taller when horizontal lines are drawn on it, i.e., Helmholtz illusion. With vertical lines curved sinusoidally, horizontal "illusory stripes" are perceived; and with horizontal lines curved sinusoidally, vertical "illusory stripes" are perceived. The purpose of the present study was to test whether the "illusory stripes" produce the Helmholtz illusion. We measured the apparent size of a square patch filled with sinusoidal lines. Our subjects (N=27) judged the patch with horizontal "illusory stripes" taller than the square patch filled with vertical straight lines. The subjects also judged the square patch with vertical "illusory stripes" wider than the square patch filled with horizontal straight lines. These results demonstrate that "illusory stripes" can produce the Helmholtz illusion.     

Orientation-contingent color aftereffects mediated by subjective transparent structures.

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n = 6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeared more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes. Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

A study of afterimages generated by monocular and dichoptic viewing

Fragmentation of a prolonged afterimage of a vertical bar viewed monocularly against a background of either horizontal or vertical stripes was investigated. The background of vertical stripes produced greater partial fragmentation of the bar than did the horizontal background. This effect was not found for binocular viewing, in which the afterimage was viewed against a background seen by the other eye. Implications for present theories of fragmentation are discussed.     

Orientation-contingent color aftereffects mediated by subjective transparent structures

We examined whether the orientation-contingent color aftereffect (the McCollough effect) could be mediated by subjective horizontal and vertical structure induced by the perception of transparency. In our experiments, red vertical bars and green horizontal bars were alternated as an adapting stimulus. After adaptation, subjects (n=6) were asked to adjust the green and red saturation of a test pattern until they obtained a neutral gray. Horizontal and vertical stripes were combined in the test pattern in three different ways: (1) overlapping with a luminance combination that gave rise to a perception of transparent overlays of horizontal and vertical stripes (valid transparency condition), (2) overlapping with luminance combinations that did not induce a perception of transparency (invalid transparency condition) and that appeased more as a patchwork of checks, and (3) presented in adjacent, nonoverlapping areas. Our results showed that the McCollough effect was significantly greater in the valid transparency condition than in the invalid transparency conditions. The effect in the valid transparency condition was nevertheless less strong than was the effect seen with the standard test stimulus made up of nonoverlapping vertical and horizontal stripes, Our results suggest that the McCollough effect can be mediated by the subjective spatial organization (inner representation of vertical and horizontal stripes) that accompanies the perception of transparency in our stimulus.     

Color-Binding Errors During Rivalrous Suppression of Form

ABSTRACT— How does a physical stimulus determine a conscious percept? Binocular rivalry provides useful insights into this question because constant physical stimulation during rivalry causes different visual experiences. For example, presentation of vertical stripes to one eye and horizontal stripes to the other eye results in a percept that alternates between horizontal and vertical stripes. Presentation of a different color to each eye (color rivalry) produces alternating percepts of the two colors or, in some cases, a color mixture. The experiments reported here reveal a novel and instructive resolution of rivalry for stimuli that differ in both form and color: perceptual alternation between the rivalrous forms (e.g., horizontal or vertical stripes), with both eyes' colors seen simultaneously in separate parts of the currently perceived form. Thus, the colors presented to the two eyes (a) maintain their distinct neural representations despite resolution of form rivalry and (b) can bind separately to distinct parts of the perceived form.     

Transfer after pretraining with the negative stimulus

Two groups of rats trained in the jumping stand acquired a horizontal stripes vs. vertical stripes discrimination and then learned its reversal. The groups differed in their pretraining. One group had previously learned a black vs. white discrimination; the other a discrimination in which the S- was the same as that used in the horizontal against vertical problem. S- pretraining facilitated not only acquisition but also the reversal of the orientation discrimination thereby confirming a prediction that reversal learning will be rapid when the original problem is learned chiefly in terms of the S-. It is suggested that overtraining may facilitate reversal learning, in some cases at least, by inducing animals to concentrate on the S-.     

Surface and Edge Information for Spatial Integration: A Saccadic-selection Search Task

Three experiments are described that investigate visual integration across space using a saccade selection paradigm. Subjects saccaded to a vertical target in the presence of a number of horizontal distractor items. Both horizontal and vertical items were composed of two identical elements, so, in order to locate the target, subjects had to integrate the pairs of elements together. We measured saccade accuracy, the proportion of saccades directed to the vertical target, together with saccade latency following display appearance. In Experiment 1 we found that saccade accuracy was improved by the items having either common surface properties or collinear edges. These effects were not a resultof increased display heterogeneity (Experiment 2), or a result of the introduction of a strong internal contour between the items (Experiment 3). These results show that for saccadic selection both surface and edge properties of items are processed. This in turn suggests thatearly visual processing encodes and exploits both types of information.     

Emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations in rats

The present experiment investigated whether rats formed emergent, untrained stimulus relations in many-to-one matching-to-sample discriminations. In Phase 1, rats were trained to match two samples (triangle and horizontal stripes) to a common comparison (horizontal stripes) and two additional samples (circle or vertical stripes) to another comparison (vertical stripes). Then, in Phase 2, the rats were trained to match the one sample (triangle) to a new comparison (black) and the other sample (circle) to another comparison (white). In the Phase 3 test, half the rats (consistent group) were given two new tasks in which the sample-correct comparison relation was consistent with any emergent stimulus relations that previously may have been learned. The remaining 6 rats (inconsistent group) were given two new tasks in which the sample-correct comparison relation was not consistent with any previously learned emergent stimulus relations. Rats in the consistent group showed more accurate performance at the start of Phase 3, and faster learning to criterion in this phase, as compared with rats in the inconsistent group. This finding suggests that rats may form emergent, untrained stimulus relations between the discriminative stimuli in many-to-one matching-to-sample discriminations.     

Comparison between the lambda response of eye-fixation-related potentials and the P100 component of pattern-reversal visual evoked potentials

The purpose of this study was to compare the lambda response of eye-fixation-related potentials (EFRPs) with the P100 component of pattern-reversal visual-evoked potentials. EFRPs were obtained by averaging EEGs time-locked to the offset of the saccade. The dipole of the lambda response and that of the P100 component were estimated by the dipole-tracing method (Musha & Homma, 1990). The locations of their dipoles at the occipital sites were very close to each other when the difference waveform, which was calculated by subtracting the EFRP to the patternless stimulus from the EFRP to the patterned stimulus, was used for the lambda response. This finding implies that the lambda response and P100 have a common neural generator in the visual cortex. However, the peak latency of the lambda response was shorter than that of P100. The saccades in the EFRP trial were considered to be the cause of the difference.     

Visual exploration pattern in hemineglect

The analysis of eye movement parameters in visual neglect such as cumulative fixation duration, saccade amplitude, or the numbers of saccades has been used to probe attention deficits in neglect patients, since the pattern of exploratory eye movements has been taken as a strong index of attention distribution. The current overview of the literature of visual neglect has its emphasis on studies dealing with eye movement and exploration analysis. We present our own results in 15 neglect patients. The free exploration behavior was analyzed in these patients presenting 32 naturalistic color photographs of everyday scenes. Cumulative fixation duration, spatial distribution of fixations in the horizontal and vertical plane, the number and amplitude of exploratory saccades was analyzed and compared with the results of an age-matched control group. A main result of our study was that in neglect patients, fixation distribution of free exploration of natural scenes is not only influenced by the left–right bias in the horizontal direction but also by the vertical direction.     

Further studies of the McCollough effect

Following prolonged viewing of black and white striped pattems in colored light, red and green aftereffects that lasted as long as 3 days were seen on the patterns, illuminated with white light. Altemate exposures of a vertical pattern of stripes in green light and a horizontal in white light (or a vertical in white light and a horizontal in red light) produced a red aftereffect on the vertical pattern and a green on the horizontal. The red and green aftereffects were also produced with a single vertical pattern. Adaptation colors that were at all greenish produced a red aftereffect on a vertical pattern and a green on a horizontal, whereas colors that were at all reddish produced a green aftereffect on a vertical pattern and a red on a horizontal. Colors near pure blue and pure yellow, which had little red or green content, produced weak aftereffects. The saturation of the aftereffects on the vertical grating varied in proportion to the red or green content of the adaptation color. Vivid red and green aftereffects were frequently obtained with the vertical and horizontal adaptation patterns paired with colors that closely bracketed pure yellow or pure blue. In all cases, the aftereffects gradually desaturated as the head was gradually tilted down to the side; the colors on each test pattern, vertical and horizontal, vanished at 45-deghead tilt and reversed beyond 45 deg.     

Shift and deviate: Saccades reveal that shifts of covert attention evoked by trained spatial stimuli are obligatory

The premotor theory of attention predicts that motor movements, including manual movements and eye movements, are preceded by an obligatory shift of attention to the location of the planned response. We investigated whether the shifts of attention evoked by trained spatial cues (e.g., Dodd & Wilson, 2009) are obligatory by using an extreme prediction of the premotor theory: If individuals are trained to associate a color cue with a manual movement to the left or right, the shift of attention evoked by the color cue should also influence eye movements in an unrelated task. Participants were trained to associate an irrelevant color cue with left/right space via a training session in which directional responses were made. Experiment 1 showed that, posttraining, vertical saccades deviated in the direction of the trained response, despite the fact that the color cue was irrelevant. Experiment 2 showed that latencies of horizontal saccades were shorter when an eye movement had to be made in the direction of the trained response. These results demonstrate that the shifts of attention evoked by trained stimuli are obligatory, in addition to providing support for the premotor theory and for a connection between the attentional, motor, and oculomotor systems.     

Squinting with the mind’s eye: Effects of stimulus resolution on imaginal and perceptual comparisons

Subjects either viewed or visualized arrays that were divided into four quadrants, with each quadrant containing a set of stripes. In two experiments, one array contained only relatively narrow (high-resolution) stripes, and one contained only relatively thick (low-resolution) stripes. The subjects compared sets of stripes in different quadrants according to their length, spacing, orientation, or width. When the subjects visualized the arrays, they required much more time to compare high-resolution patterns than low-resolution patterns; when the subjects saw the arrays, they evaluated both types of arrays equally easily. In addition, the results from the third experiment provide strong evidence that people use imagery in this task; in one condition, the subjects evaluated oblique sets of stripes, and in another condition, they evaluated vertical and horizontal stripes. In both imagery and perception, the subjects made more errors when evaluating oblique stimuli; in imagery, they also required more time to evaluate oblique stimuli. The results suggest that additional effort is required in imagery to represent visual patterns with high resolution. This finding demonstrates that, although imagery and perception may activate common brain regions, it is more difficult to represent high-resolution information in imagery than in perception.     

Infant attention and the development of smooth pursuit tracking.

The effect of attention on smooth pursuit and saccadic tracking was studied in infants at 8, 14, 20, and 26 weeks of age. A small rectangle was presented moving in a sinusoidal pattern in either the horizontal or vertical direction. Attention level was distinguished with a recording of heart rate. There was an increase across age in overall tracking, the gain of the smooth pursuit eye movements, and an increase in the amplitude of compensatory saccades at faster tracking speeds. One age change was an increase in the preservation of smooth pursuit tracking ability as stimulus speed increased. A second change was the increasing tendency during attentive tracking to shift from smooth pursuit to saccadic tracking when the stimulus speed increased to the highest velocities. This study shows that the development of smooth pursuit and targeted saccadic eye movements is closely related to the development of sustained attention in this age range.     

Background stripes affect apparent speed of rotation

A gray line that rotated about its own center against a stationary background of vertical stripes appeared to double in perceptual speed as it rotated through the vertical position and thus momentarily aligned with the background. Four factors may contribute to this speed-up: (i) landmarks, in which the tip of the moving vertical line moves horizontally across the maximum number of stationary stripes; (ii) orientation repulsion of the moving line by the vertical stripes, which may distort the line's perceived position and hence its perceived speed; (iii) the orientation of an induced brightness pattern along the line; and (iv) the motion of the induced brightness pattern, which moves physically most rapidly along the line when the line is near vertical. To test these possibilities, an annulus display provided landmarks but no intersections, and this almost abolished the effect. A rotating-slit display provided an oriented, moving pattern that mimicked the induced brightness but had no landmarks, and this increased the effect. We conclude that the motion, but not the orientation, of the intersections [option (iv)] was responsible for the illusion. The fact that this motion along the length of the line affected the perceived speed of the line orthogonal to its own length indicates a failure on the part of the visual system to fully decouple tangential from radial motion.     

Footsteps and inchworms: illusions show that contrast affects apparent speed

A horizontal grey bar that drifts horizontally across a surround of black and white vertical stripes appears to stop and start as it crosses each stripe. A dark bar appears to slow down on a black stripe, where its edges have low contrast, and to accelerate on a white stripe, where its edges have high contrast. A light-grey bar appears to slow down on a white stripe and to accelerate on a black stripe. If the background luminances at the leading and trailing edges of the moving bar are the same, the bar appears to change speed, and if they are different the bar appears to change in length. A plaid surround can induce 2-D illusions that modulate the apparent direction, not just the speed, of moving squares. Thus, the motion salience of a moving edge depends critically on its instantaneous contrast against the background.     

Vertical versus horizontal spatial compatibility: Right-left prevalence with bimanual responses

For two-choice tasks in which stimulus and response locations vary along horizontal and vertical dimensions, the spatial compatibility effect is often stronger on the horizontal than vertical dimension. Umiltà and Nicoletti [(1990) Spatial stimulus-response compatibility (pp. 89–116). Amsterdam: North-Holland] attributed this right-left prevalence effect to an inability to code vertical location when horizontal codes are present simultaneously. Hommel [(1996) Perception & Psychophysics, 43, 102–110] suggested instead that it reflects a voluntary strategy. This study reports four experiments that examine this issue. Experiment 1 was a conceptual replication of Hommel's Experiment 1, with responses made on a numeric keypad and subjects instructed in terms of the vertical or horizontal dimension. The results replicated Hommel's findings that showed a right-left advantage with horizontal instructions; however, with vertical instructions, we found a benefit of vertical compatibility alone that he did not. This benefit for vertical compatibility alone was eliminated in Experiment 2 using a varied practice schedule similar to that used by Hommel. Experiment 3 showed right-left prevalence and a benefit of vertical compatibility alone, even with varied practice and vertical instructions, when subjects responded on perpendicularly arranged handgrips. These benefits were eliminated in Experiment 4 using Hommel's method of urging subjects to respond only in terms of the instructed dimension. With bimanual responses, right-left prevalence is a robust phenomenon that is evident when comparing across vertical and horizontal instructions and, when the right-left distinction is relatively salient, within the vertical instructions condition alone. Received: 4 February 2000 / Accepted: 5 May 2000     

Recording horizontal rotations of head and eyes in spontaneous shifts,of gaze

In this paper, a method is described for simultaneous recording of horizontal rotation of the eyes in the head and rotation of the head about its natural vertical axis. Angular positions of eyesand head are obtained as proportionate dc voltages that are summed to obtain a record of the horizontal direction of gaze sensitive to l-deg saccades and accurate to within ±2 deg for at least the central 90 deg of the visual field. The apparatus is so light that it is hardly felt by the S, who, while seated, is free to move in any way he chooses and to perform any task. In addition, the angular position of a target rotating around the head may also be recorded for observation of visual-pursuit behavior.     

Visual Cues Generated During Action Facilitate 14-Month-Old Infants’ Mental Rotation

Although action experience has been shown to enhance the development of spatial cognition, the mechanism underlying the effects of action is still unclear. The present research examined the role of visual cues generated during action in promoting infants’ mental rotation. We sought to clarify the underlying mechanism by decoupling different aspects of action experience and choosing to manipulate the visual aspect while holding other aspects constant. Fourteen-month-old infants were given opportunities to rotate a cylinder placed on a turntable; the cylinder was decorated with vertical or horizontal stripes. If the effects of action hinge on the quality of visual cues generated during action, infants should benefit more from rotating the cylinder with vertical stripes as they generate richer cues when each stripe moves laterally with the cylinder. As predicted, the infants in the vertical-stripe condition looked significantly longer at an improbable outcome than at a probable outcome of a hidden-rotation event, whereas those in the horizontal-stripe condition looked about equally at the 2 outcomes. The results suggest that the effects of action on mental rotation are derived not from motor experience alone, but from integrating motor and visual experiences.