Pressure blindness and the interocular transfer of size aftereffects

After observation of a stimulus composed of a top grating with large bar widths (low spatial frequency) and a bottom grating of narrow lines (high spatial frequency), a subsequently presented test grating of medium bar width appears to have a higher spatial frequency on the top half than on the bottom. Although this size aftereffect can be obtained dichoptically, this does not necessarily imply a central locus, since retinal input from the adapted eye could produce the effect. Ss were tested for the aftereffect in the adapted eye and for interocular transfer with and without pressure blinding the adapted eye. In this last condition, input from the adapted eye cannot reach the cortex. However, the aftereffect was equally present under all three conditions. This result suggests that size and frequency adaptation have a central locus.     

Illusory motion produced by dichoptic stimuli during saccades

A new motion illusion is reported in which saccadic eye movements can produce a perceived jump of a static stimulus presented dichoptically. In three experiments, observers made saccades while viewing a stationary stimulus consisting of a disk and random dots presented separately to the two eyes. In experiments 1 and 2, by measuring the strength of the perceived motion and the velocity of binocular eye movements, we found that (a) motion ratings were high for the stimulus that contained a large interocular difference in luminance, and (b) the saccadic strategy of the observer was virtually identical across different stimulus conditions. In experiment 3, by measuring the detectability of a short temporal gap introduced into the stimulus around saccades, we found that saccadic suppression was normal in the dichoptic presentation. We discuss possible mechanisms underlying the illusory motion.     

Experiments on the locus of induced motion

Two experiments examined the locus of induced motion effects. The first used a subjective technique to test for the presence of retinal slippage due to systematic eye movements when an observer fixates a test spot in the center of a horizontally moving rectangle. The second experiment tested for “local” retinal effects by presenting test and inducing figures dichoptically. There was no evidence of retinal slippage under conditions where induced motion was not discriminable from real motion. Moreover, good induction was produced across eyes. Implications for the locus of induced motion effects are discussed.     

Dichoptic induction of movement aftereffects contingent on color and on orientation

Some comparative experiments on the dichoptic induction of the movement aftereffect (MAE) contingent on color and the MAE contingent on orientation are reported. Colorcontingent movement aftereffects could be evoked only when the eye which had viewed color during adaptation also viewed color during test sessions. When the apparent color of the test field was changed by binocular color rivalry, contingent movement aftereffects (CMAEs) appropriate to the suppressed color were reported. After dichoptic induction of the orientation-contingent MAE, aftereffects could be obtained whether the eliciting gratings and stationary test fields were presented together to either eye alone or were dichoptically viewed.     

Dichoptic induction of Mccollough-type effects

If left-oblique and right-oblique black/white gratings are presented alternately to one eye, and unpatterned red and green fields are presented alternately to the other, orientation-sensitive chromatic after-effects are induced. With the colour-stimulated eye the hue usually seen on a test grating is complementary to that originally paired with its orientation, with the pattern-stimulated eye the hue is the same as that originally paired.

The experiments reported here show that: (a) the time course of decay of these chromatic after-effects (for each eye) fits approximately the same power law as that found for the normal McCollough effect; (b) analogous chromatic after-effects, opposite in the two eyes, can be dichoptically induced using pairs of stimuli other than gratings, such as dot patterns differing in magnification.

These results suggest that strongly coloured light in one eye can induce a weakly complementary bias in the colour-signalling system of the other eye, at a level peripheral to the site of the McCollough-type adaptation.     

The “lag effect” in dichoptic viewing

Ten subjects were asked to report both of two different consonant-vowels (CVs) presented to the same foveal area, but in different eyes (“dichoptically”). Stimuli were presented at stimulus-onset asynchronies (SOAs) ranging from 0 to 150 msec in 25-msec steps. Correct identifications were significantly depressed for the eye receiving the leading stimulus at SOAs of 25 to 75 msec. Monoptic data from three subjects indicated no significant reductions in correct identification as a function of SOA. The dichoptic results can be understood in terms of current theories of visual backward masking and are similar to the “lag effect” observed with dichotic listening to speech stimuli. Similarity of results for the two modalities suggests a similar “two-process” explanation may underlie both phenomena.     

Differential resistance to distortion as a functional property of two structural parameters of two dimensional line drawings

Two structural parameters of two dimensional drawings, sidedness and regularity, are systematically varied and their relationship to the breakdown of binocular fusion (doubling of image) as a function of increasing lateral separation of dichoptically presented images is explored. Sidedness is not found to be systematically significant parameter, while regularity is seen to operate across figures (independently of sidedness). A predictive analysis, in terms of the Gestalt variables of “good form” is examined, and the results discussed in terms of these variables, a personality dimension and uncertainty.     

Perceiving surfaces in depth beyond the fusion limit of their elements

An isolated dot appears double outside a small disparity range called Panum's fusional area. In random-dot stereograms (RDSs), however, this doubling, or diplopia of dot elements is not evident at any disparity. Nevertheless, depth is perceived up to disparities that greatly exceed Panum's fusional limit. Either one is unaware of dot diplopia at disparities exceeding Panum's fusional limit or the fusion limit is extended. To examine these possibilities, we developed a novel RDS in which dichoptically color-coded dots have a distinctive color when fused, and return to their intrinsic colors when diplopic. We measured the fusion limit of dots in this RDS, and compared it to the patent stereopsis limit of the perceived surface in similar RDSs. We found that the fusional area of dots in the RDS was comparable to Panum's fusional area. Furthermore, there was clear dissociation between the fusion limit and the patent stereopsis limit in the RDS. We conclude that the elements composing a surface are not necessarily fused when a large disparity surface is perceived in depth.     

Discrimination of stimulus aperiodicity as a function of temporal patterning: a discrepancy between psychophysical and sensory-neural assessments.

Tactile discrimination of stimulus aperiodicity was investigated in a two-alternative forced-choice task by having subjects report which of two successively presented trains of mechanical pulses, one with complete pulse periodicity and one in which a single pulse was temporally displaced from its regular placement, was temporally irregular or aperiodic. Trains contained three, four, or five pulses and were presented at interpulse intervals of 60, 75, 85, 100, 125, and 150 ms. Aperiodic trains had one pulse, other than the first or last pulse, temporally advanced or receded by 40% of the interstimulus interval. Results showed that: (i) although the percentage of correct reports of aperiodicity decreased as presentation rate increased (smaller interpulse intervals), the amount of decrease was a function of the number of pulses in a train; (ii) the discrimination of aperiodicity was dependent upon the specific location of the irregularity within the stimulus temporal pattern; and (iii) all patterns with complete temporal reversals of their successive interpulse intervals yielded nearly equivalently accurate reports of aperiodicity. These data suggest that central, attentional factors are involved in the discrimination of stimulus aperiodicity.     

Unconscious processing of dichoptically masked words

In three experiments, the subjects' task was to decide whether each of a series of words connoted something good (e.g., fame, comedy, rescue) or bad (stress, detest, malaria). One-half second before the presentation of each such target word, an evaluatively polarized priming word was presented briefly to the nondominant eye and was masked dichoptically by either the rapidly following (Experiment 1) or simultaneous (Experiments 2 and 3) presentation of a random letter-fragment pattern to the dominant eye. (The effectiveness of the masking procedure was demonstrated by the subjects' inability to discriminate the left vs. right position of a test series of words.) In all experiments, significant masked priming effects were obtained; evaluative decisions to congruent masked prime-target combinations (such as a positive masked prime followed by a positive target) were significantly faster than those to incongruent (e.g., negative prime/positive target) or noncongruent (e.g., neutral prime/positive target) combinations. Also, in two of the three experiments, when subjects were at chance accuracy in discriminating word position, their position judgments were nevertheless significantly influenced by the irrelevant semantic content (LEFT vs. RIGHT) of the masked position-varying words. The series of experiments demonstrated that two very different tasks--speeded judgment of evaluative meaning and nonspeeded judgment of word position--yielded statistically significant and replicable influences of the semantic content of apparently undetectable words. Coupled with previous research by others using the lexical decision task, these findings converge in establishing the reliability of the empirical phenomenon of semantic processing of words that are rendered undetectable by dichoptic pattern masking.     

The two-flash threshold: An evaluation of critical-duration and visual-persistence hypotheses

The two-flash threshold is reduced by increasing the duration of both pulses of light or light adapting the eye. Increasing the duration of the first pulse also decreases the two-flash threshold, contrary to what a critical-duration explanation of the threshold would predict. Decreasing the duration of the second pulse increases the threshold when the second pulse is very brief. Light adapting the eye under such conditions serves to increase the two-flash threshold, unlike the effect adaptation has when a long second pulse is used.     

基于直线临摹的ADHD儿童眼手协调能力研究

ADHD儿童在精细动作方面通常伴随眼手协调运动障碍。以往采用的研究方法多为定性研究,且未在ADHD儿童的运动协调性与同龄正常儿童的差异上得出统一结论。本研究针对精细动作中眼手协调能力进行定量分析。实验要求被试在计算机触摸屏上分别临摹水平线、垂直线和斜线,通过记录临摹直线与呈现直线的偏差程度和拐点数,以分析ADHD儿童眼手协调能力与正常儿童之间的差异。结果表明,ADHD儿童在眼手协调和空间知觉能力上与正常儿童存在显著性差异。此外,本研究表明,改进的定量方法具有良好的可行性。     

Influence of spatial frequency, luminance, and duration on binocular rivalry and abnormal fusion of briefly presented dichoptic stimuli

Orthogonal gratings, presented dichoptically, do not fuse into a single percept. Parts of each are seen while other parts are suppressed in an unstable perception (binocular rivalry). However, it has been previously noted that, if the gratings are briefly flashed, they will appear to fuse into a plaid or checkerboard pattern. Three experiments are reported which have been designed to define more clearly the spatial and temporal parameters of this effect in the hope that this would lead to better understanding of the normal mechanisms of dominance and suppression. Stimuli appear fused if flashed for less than 150 ms. The effect is independent of substantial changes in spatial frequency and luminance. Single flashes that appear fused when presented in isolation produce rivalry if separated by intervals less than about 150 ms. Intervals greater than 150 ms produce continued abnormal fusion. Possible mechanisms are discussed.     

Involvement of IP3 receptors in LTP and LTD induction in guinea pig hippocampal CA1 neurons

The role of inositol 1, 4, 5-trisphosphate receptors (IP3Rs) in long-term potentiation (LTP) and long-term depression (LTD) was studied in CA1 neurons in guinea pig hippocampal slices. In standard solution, short tetanic stimulation consisting of 15 pulses at 100 Hz induced LTP, while three short trains of low-frequency stimulation (LFS; 200 pulses at 1 Hz) at 18-min intervals or one long train of LFS (1000 pulses at 1 Hz) induced stable LTD in both the slope of the field EPSP (S-EPSP) and the amplitude of the population spike (A-PS). Bath application of 2-aminoethoxydiphenyl borate (2-APB), an IP3R antagonist, or of alpha-methyl-4-carboxyphenylglycine (MCPG), a wide-spectrum metabotropic glutamate receptor antagonist, during weak tetanic stimulation significantly increased the magnitude of the LTP in both the S-EPSP and A-PS. Three short trains of LFS or one long train of LFS delivered in the presence of 2-APB or MCPG did not induce LTD, but elicited LTP. Based on these results, we conclude that, in hippocampal CA1 neurons, IP3Rs play an important role in synaptic plasticity by attenuating LTP and facilitating LTD.     

Lateral visual masking: Supraretinal effects when viewing linear arrays with unlimited viewing time

Linear letter arrays of varying lengths were presented monocularly, binocularly, and dichoptically in order to provide locus information concerning previous findings that recognition of letters in such an array follows a U-shaped function over positions. With unlimited viewing time and constant fixation, U-shaped serial position curves were generated under all conditions of viewing. It was concluded that some supraretinal lateral masking effect is involved.     

Aging and the depth of binocular rivalry suppression

Two experiments were designed to examine the effect of aging on the strength of binocular rivalry suppression. To produce rivalry, orthogonally oriented sine-wave luminance gratings were presented dichoptically. The observers were then required either to discriminate the spatial location of a probe spot presented to the dominant or suppressed eye's view or to detect the presence or absence of the probe. The observers in the younger and older age groups exhibited typical rivalry suppression for both tasks (i.e., the probe was more difficult to detect or discriminate when presented to the suppressed eye), but the magnitude of the suppression was significantly larger in the older observers. This increased suppression that accompanies aging can be explained by a reduction in the inhibition produced by the binocular matching circuitry of S. R. Lehky and R. Blake's (1991) model.     

Monoptic and dichoptic metacontrasf

Metacontrast suppression was compared under conditions of monoptic and dichoptic presentation. It was found that interference was greater with dichoptic than with monoptic presentation, and that the point of maximum interference differed in the two conditions. The interference curve generated as a function of inter-stimulus interval (ISI) was also different; monoptically a “U”-shaped curve was found, whereas dichoptically the curve appeared to be more “J”-shaped. Theoretical implications are discussed, and it is suggested that binocular rivalry may play a role in dichoptic interference.     

Evidence for visual persistence during saccadic eye movements

Summary 1. The persistence of visual perception was investigated under conditions of visual fixation as well as eye movement. The Ss' task was to discriminate brief double light impulses; their responses were recorded as a function of the duration of the interstimulus interval. Based on these data the critical interstimulus interval was calculated, which yielded equal response frequencies for the perception of one or two stimuli upon presentation of double light pulses.2. In the condition of visual fixation the two stimuli could not be discriminated until the mean value of interstimulus interval exceeded 73 msec. In the condition with eye movements, when the first stimulus was presented in the parafoveal region of the retina before the beginning of the saccade and the second stimulus in the foveal region just after termination of the eye movement, this duration was shown to be statistically of the same magnitude (76 msec).3. Possible alternative interpretations of this latter result, e.g., that it could be explained in terms of masking or saccadic suppression rather than visual persistence was discussed; it was attempted to invalidate such explanations by means of three control experiments.4. The main result, the persistence of visual perception during voluntary eye movements, was discussed in relation to the problem of spatial and temporal stability of visual perception.I thank Prof. Dr. H.W. Wendt for support in correcting the English translation.     

A developmental study of the effect of eye movements on the processing of shape information

Three experiments were performed using an aperture-viewing technique to assess the accuracy of shape perception when subjects were required to emit eye movements in order to pick up shape information, compared with the accuracy of shape perception when subjects were not required to emit eye movements in order to pick up the same shape information. In two of the three experiments, we also tried to elicit two different kinds of eye movements which have been suggested as being differentially useful for the processing of shape information. All three experiments explored whether the usefulness of eye movements varied as a function of age. The results of all three experiments indicate that the accuracy of shape perception improves with age under aperture-viewing conditions. The conditions in which eye movements were required to pick up the shape information led to an improvement in the processing of the shape information. This improvement seems to be about the same for both of the eye movement conditions and for all of the age groups tested (4.6 years through 21.7 years).     

A distributed intercortical processing of binocular rivalry: psychophysical evidence

When dissimilar visual scenes are viewed dichoptically, the observer perceives several different representations of the scene over time. To reveal that a distributed intercortical network mediates this phenomenon of binocular rivalry, we used a Kanizsa square-like display consisting of four pairs of color-rivalry-inducing elements. We found that when all four dominant elements had the same color, regardless of whether they were from the same or different eyes, the visual system ably integrated them into a larger subjective surface. Once formed, the same-colored subjective surface enjoyed a relatively longer predominance than mixed-colored patterns. During rivalry alternation, this same-colored surface was more likely to be replaced by a complementary same-colored surface, rather than by mixed-colored patterns (cohesive effect). Further, surface integration, which is mainly an extrastriate cortical function, was stronger when the same eye viewed the same-colored rivalry stimuli. Since the eye-of-origin signature is explicitly represented in V1, these findings together suggest that rivalry is processed along a distributed network including V1 and the extrastriate cortices.