Perceptual aftereffects of sustained convergence

Attention, Perception, & Psychophysics - Fixating a target for 6 or 8 min was shown to produce distance aftereffects that varied in direction (i.e., over- or underestimation) and magnitude as a...     

Perceptual asymmetries associated with changing-loudness aftereffects

Listening to decreasing sound level leads to an increasing-loudness aftereffect, whereas listening to increasing sound level leads to a decreasing-loudness aftereffect. Measuring the aftereffects by nulling them in short test stimuli reveals that increasing-loudness aftereffects are greater than decreasing-loudness aftereffects. However, this perceptual asymmetry may be due to another illusion--the growing-louder effect: In the absence of any adaptation, short steady stimuli are heard as growing louder. In an experiment in which the duration of test stimuli varied from 1.0 to 2.5 sec, the growing-louder effect did not occur in the longer test stimuli, but the asymmetry in changing-loudness aftereffects remained. The aftereffect asymmetry is therefore independent of the growing-louder effect. The aftereffect asymmetry is consistent with other psychophysical and physiological evidence that is believed to concern potential collision: An approaching sound-source elicits increasing sound level. In addition, the aftereffect asymmetry parallels a well-known asymmetry regarding aftereffects of visual motion, which is also attributed to potential collision.     

Perceptual, oculomotor, and neural responses to moving color plaids

Moving plaids constructed from two achromatic gratings of identical luminance contrast are known to yield a percept of coherent pattern motion, as are plaids constructed from two identical chromatic (e.g. isoluminant red/green) gratings. To examine the interactive influences of chromatic and luminance contrast on the integration of visual motion signals, we constructed plaids with gratings that possessed both forms of contrast. We used plaids of two basic types, which differed with respect to the phase relationship between chromatic and luminance modulations (after Kooi et al, 1992 Perception 21 583-598). One plaid type ('symmetric') was made from component gratings that had identical chromatic/luminance phase relationships (e.g. both components were red-bright/green-dark modulation). The second plaid type ('asymmetric') was made from components that had complimentary phase relationships (i.e. one red-bright/green-dark grating and one green-bright/red-dark grating). Human subjects reported that the motion of symmetric plaids was perceptually coherent, while the components of asymmetric plaids failed to cohere. We also recorded eye movements elicited by both types of plaids to determine if they are similarly affected by these image cues for motion coherence. Results demonstrate that, under many conditions, eye movements elicited by perceptually coherent vs noncoherent plaids are distinguishable from one another. To reveal the neural bases of these perceptual and oculomotor phenomena, we also recorded the responses of neurons in the middle temporal visual area (area MT) of macaque visual cortex. Here we found that individual neurons exhibited differential tuning to symmetric vs asymmetric plaids. These neurophysiological results demonstrate that the neural mechanism for motion coherence is sensitive to the phase relationship between chromatic and luminance contrast, a finding which has implications for interactions between 'color' and 'motion' processing streams in the primate visual system.     

Disturbance of the oculomotor system due to lateral fixation

Three experiments are reported on the effects of previous lateral deviation of the eyes. There is a large effect on their subsequent resting position, and a smaller instantaneous effect on voluntary eye centring. Both are in the direction of previous fixation. The latter effect becomes insignificant within 30 s. The treatment produces errors in visually guided reaching away from the previous direction of fixation. The effects are consistent with a change in registered eye position, an effect also produced by exposure to prisms. Despite this similarity, the disturbance to the oculomotor system caused by these two treatments is sharply differentiated by the resting position. Prisms cause subsequent low frequency, high amplitude oscillations of the eyes (Craske and Templeton, 1968), whereas following lateral deviation the mean resting position returns gradually towards the pre-treatment position.     

Perceptual changes in taste mixtures

Three studies were conducted to quantify perceptual changes that occur when sapid chemicals are tasted in mixture solutions. The primary effect when mixing sweetness (glucose or fructose) with salt (NaCl), sour (citric acid), or bitter (quinine sulfate) was to reduce the intensity of each taste in the mixture. The reduction was not equal for the two components, although the overall (total) taste intensity of the mixture appeared to be approximately 50% of the sum of the intensities of the unmixed components. Mixtures of sweet and salt developed an “unblended” or “clashing” taste, in which the components alternated in attempting to dominate the taste percept. Sweet mixed with either sour or bitter blended in almost all proportions. The “flavor” of sweetness in mixtures differed from that of simple sugar sweetness, suggesting that the presence of a second taste modified the qualitative aspect of sweetness. The magnitude of change in sweetness quality depended upon the sugar being rated, and upon the quality and intensity of the second, or modifying, taste.     

Developmental changes in oculomotor control and working-memory efficiency

In the present study, we examined the developmental changes in the efficiency of saccadic inhibitory control. More specifically, the contribution of age-related changes in working-memory engagement was investigated. We manipulated the efficiency of inhibitory oculomotor control in antisaccade tasks by using fixation-offset conditions, which are supposed to affect inhibitory demands, and by adding increasing working-memory loads to the antisaccade task. In general, in comparison to antisaccade performance of adults, the antisaccade performance of 8-year-old and 12-year-old children was characterized by an increase in direction errors, and/or longer saccadic onset latencies on correct antisaccades. However, this pattern was not altered by the fixation-offset manipulations. In contrast, increased working-memory demands deteriorated 8-year-olds' antisaccade performance unequally as compared to older children and young adults. These findings suggest that - at least in young children - the available functional working-memory capacity is engaged in oculomotor inhibition.     

Concomitant direction and distance aftereffects of sustained convergence: A muscle potentiation explanation for eye-specific adaptation

Fixating a target for 6 min was shown to produce distance aftereffects that varied in direction and magnitude as a linear function of the convergence angle. Eye-specific direction aftereffects also were obtained in a nasal direction under conditions that produce increased perceived distance and in a temporal direction under conditions that produce decreased perceived distance. These aftereffects were shown to be sensitive to the range of horizontal versional eye movements that accompany the near or far convergence positions maintained during exposure. The results provide a logical alternative to perceptual learning accounts of eye-specific adaptation.     

Art and the oculomotor system: perspective illustrations evoke vergence changes

When a painting or drawing is viewed monocularly and fixation alternated between points that are at different implied distances from the observer, the covered eye usually makes vergence movements that are directionally appropriate for the indicated depth differences. These vergence changes evoked by perspective artwork vary greatly in magnitude and consistency from one illustration to the next: some drawings and paintings lead to convergence-divergence changes smaller than would be appropriate for the illustrated content, if seen from the implied viewing distance; others are supernormal stimuli, evoking inappropriately large vergence changes in all observers tested.     

The effects of saccade-contingent changes on oculomotor capture: salience is important even beyond the first oculomotor response

Whenever a novel scene is presented, visual salience merely plays a transient role in oculomotor selection. Unique stimulus properties, such as a distinct and, thereby, salient color, affect the oculomotor response only when observers react relatively quickly. For slower responses, or for consecutive ones, salience-driven effects appear completely absent. To date, however, the circumstances that may reinstate the effects of salience over multiple eye movements are still unclear. Recent research shows that changes to a scene can attract gaze, even when these changes occur without a transient signal (i.e., during an eye movement). The aim of the present study was to investigate whether this capture is mediated through salience-driven or memory-guided processes. In three experiments, we examined how the nature of a change in salience that occurred during an eye movement affected consecutive saccades. The results demonstrate that the oculomotor system is exclusively susceptible to increases in salience from one fixation to the next, but only when these increases result in a uniquely high salience level. This suggests that even in the case of a saccade-contingent change, oculomotor selection behavior can be affected by salience-driven mechanisms, possibly to allow the automatic detection of uniquely distinct objects at any moment. The results and implications will be discussed in relation to current views on visual selection.     

Monocular-contingent and binocular-contingent aftereffects

Alternate monocular and binocular exposure to complementary stimulation can yield opposite but coexisting aftereffects that are contingent on whether the test display is viewed with one eye or two eyes. The motion aftereffect was studied by adapting each eye separately to a contracting spiral and both eyes together to an expanding spiral. The stationary test spiral subsequently appeared to be expanding when viewed monocularly, but to be contracting when it was seen with both eyes open. With respect to the McCollough effect, after monocular exposure to red-vertical and green-horizontal gratings and binocular exposure to red-horizontal and green-vertical gratings, the appearance of the color of the test gratings when viewed with one eye was different from that when viewed with both eyes. Opposite, coexisting aftereffects induced by complementary stimulation can be interpreted as evidence that there are unique binocular aspects to visual function.     

知觉经验与知觉内容

知觉(perception)是指我们通过视觉、听觉、触觉、嗅觉、味觉等感觉器官而获得的对事物以及外部世界的意识感知.知觉经验(perceptual experience)的一个显著的特点是它具有某种现象特征,即知觉者会体验到一种"那究竟像什么(what it is like)"的感觉.例如,一个人会从红色视觉经验中体验到"红色究竟像什么"的意识感受性(qualia).知觉内容(perceptual content)粗略地讲是指通过知觉经验向知觉者所传递的信息.关于知觉问题在哲学上的重要性,我们可以从以下几点来看:在形而上学方面,知觉是我们了解外部物理世界究竟存在什么的主要手段;在认识论方面,研究知觉是研究我们如何达到关于外部物理世界的知识的主要手段;在语言哲学方面,知觉内容是我们的心灵与外部物理世界的关联及互动在语言实践上的体现;在心灵哲学方面,知觉经验中的现象特征与意识及意向性之间存在着深层的内在联系.     

Immediate priming and cognitive aftereffects

Three forced-choice perceptual word identification experiments tested the claim that transitions from positive to negative priming as a function of increasing prime duration are due to cognitive aftereffects. These aftereffects are similar in nature to perceptual aftereffects that produce a negative image due to overexposure and habituation to a stimulus. Each experiment tested critical predictions that come from including habituation in a dynamic neural network with multiple levels of processing. The success of this account in explaining the dynamics of repetition priming, associative-semantic priming, and forward masking effects suggests that habituation is a useful mechanism for reducing source confusion between successively presented stimuli. Implications are considered for visible persistence, repetition blindness, attention-based negative priming, attentional blink, inhibition of return, the negative compatibility effect, affect priming, and flanker preview effects.     

Motion aftereffects and retinal motion

Two experiments are described in which it was investigated whether the adaptation on which motion aftereffects (MAEs) are based is a response to retinal image motion alone or to the motion signal derived from the process which combines the image motion signal with information about eye movement (corollary discharge). In both experiments observers either fixated a stationary point or tracked a vertically moving point while a pattern (in experiment 1, a grating; in experiment 2, a random-dot pattern) drifted horizontally across the field. In the tracking condition the adapting retinal motion was oblique. In the fixation condition it was horizontal. In every case in both conditions the MAE was horizontal, in the direction opposite to that of pattern motion. These results are consistent with the hypothesis that the adaptation is a response to the motion signal derived from the comparison of eye and image motion rather than to retinal motion per se. An alternative explanation is discussed.     

Effects and aftereffects of stressor expectations

Is stressor exposure necessary to produce "stress" effects, or can these effects result from stressor anticipation alone? The present research explores whether it is possible to obtain "stress responses" during and after the period in which stressor exposure is being anticipated. In the first study, the expectation of submerging one's hand in ice water resulted in decreased frustration tolerance and increased blood pressure when compared with control groups not expecting this stressor. A second study replicated and extended these results to show that the expectation of control over the stressor ameliorates the negative impact of stressor expectation. The second study also examined the aftereffects of expectations. Particularly, it found that despite being relieved of the expectation that they would immerse their hand in ice water, subjects who had expected stressor exposure had decreased frustration tolerance when compared with either subjects who had expected a nonstressful procedure or those who had expected to have control over stressor termination. A third study, using noise as the expected stressor, replicated both the aftereffect of the anticipation period and the moderation of that effect by perceived control. The discussion (a) focuses on the implications of this work for understanding why aftereffects occur and (b) proposes that previously observed stressor exposure effects may in fact be postexpectation effects.