Detection of changes in speed and direction of motion: Reaction time analysis

Observers reacted to the change in the movement of a random-dot field whose initial velocity,V _o, was constant for a random period and then switched abruptly to another value,V ₁. The two movements, both horizontally oriented, were either in the same direction (speed increments or decrements), or in the opposite direction but equal in speed (direction reversals). One of the two velocities,V ₀ orV ₁, could be zero (motion onset and offset, respectively). in the range of speeds used, 0–16 deg/sec (dps), the mean reaction time (MRT) for a given value ofV ₀ depended on |V ₁-V ₀| only: MRT ≈r +c(V ₀/|V ₁ ?V ₀|) ^β , where β=2/3,r is a velocity-independent component of MRT, andc(V ₀) is a parameter whose value is constant for low values ofV ₀ (0–4 dps), and increases beginning with some value ofV ₀ between 4 and 8 dps. These and other data reviewed in the paper are accounted for by a model in which the time-position function of a moving target is encoded by mass activation of a network of Reichardt-type encoders. Motion-onset detection (V ₀=0) is achieved by weighted temporal summation of the outputs of this network, the weights assigned to activated encoders being proportional to their squared spatial spans. By means of a “subtractive normalization,” the visual system effectively reduces the detection of velocity changes (a change fromV ₀ toV ₁) to the detection of motion onset (a change from 0 toV ₁-V ₀). Subtractive normalization operates by readjustment of weights: the weights of all encoders are amplified or attenuated depending on their spatial spans, temporal spans, and the initial velocityV ₀. Assignment of weights and weighted temporal summation are thought of as special-purpose computations performed on the dynamic array of activations in the motion-encoding network, without affecting the activations themselves.     

Infants' perception of subjective contours from apparent motion

We examined infants' perception of subjective contours in Subjective-Contour-from-Apparent-Motion (SCAM) stimuli [e.g., Cicerone, C. M., Hoffman, D. D., Gowdy, P. D., & Kim, J. S. (1995). The perception of color from motion. Perception & Psychophysics, 57, 761-777] using the preferential looking technique. The SCAM stimulus is composed of random dots which are assigned two different colors. Circular region assigned one color moved apparently, keeping all dots' location unchanged. In the SCAM stimulus, adults can perceive subjective color spreading and subjective contours in apparent motion (http://c-faculty.chuo-u.ac.jp/ approximately ymasa/okamura/ibd_demo.html). In the present study, we conducted two experiments by using this type of SCAM stimulus. A total of thirty-six 3-8-month-olds participated. In experiment 1, we presented two stimuli to the infants side by side: a SCAM stimulus consisting of different luminance, and a non-SCAM stimulus consisting of isoluminance dots. The results indicated that the 5-8-month-olds showed preference for the SCAM stimuli. In experiments 2 and 3, we confirmed that the infants' preference for the SCAM stimulus was not generated by the local difference and local change made by luminance of dots but by the subjective contours. These results suggest that 5-8-month-olds were able to perceive subjective contours in the SCAM stimuli.     

Perceptual learning on inspection time and motion perception

Perceptual learning on simple perceptual tasks is interpreted as plasticity of neuronal populations in the sensory cortex (M. Fahle & T. Poggio, 2002). The authors examined individual differences on perceptual learning for 2 tasks-inspection time (IT) and a motion direction discrimination task that was instantiated as random dot kinematograms. The authors' main questions were whether individual differences in perceptual learning were consistent across the 2 tasks and whether perceptual learning correlated with cognitive abilities test scores. In all, 56 young adults completed 16 threshold estimations on 1 of 2 orthogonal versions of each task. Then, the authors made 2 further threshold estimations for the untrained, orthogonal version. Participants also completed a battery of 6 cognitive abilities tests that measured fluid ability (Gf) and perceptual speed (Gs). Perceptual learning was demonstrated for both tasks, but the degree of learning across tasks was not characteristic of the individual. Learning on IT correlated with Gs (r = .35), but learning on the motion direction discrimination task was unrelated to cognitive ability. Correlations of IT with cognitive measures were stable over the training period. IT was correlated with both the motion direction discrimination task (r = -.39) and an unmasked line length judgment task (r = -.31). The authors concluded that perceptual learning on IT correlates with cognitive abilities test scores, that correlations of IT with cognitive abilities test scores are stable as task performance improves with practice, and that the IT task is psychologically complex.     

Integration of speed signals in the direction of motion

Speed discrimination tasks were used to examine the spatial and temporal characteristics of the integration mechanism involved when signals are extended in the direction of motion. We varied the aspect ratio of a signal patch whose speed differed from the background, while holding the area of the signal patch constant, so that the signal patch could be either extended in the direction of motion or extended orthogonal to the direction of motion. Speed discrimination thresholds decreased dramatically as the signal patch was extended in the direction of motion. The spatial and temporal integration regions were larger than would be expected if the integration mechanism were a low-level motion detector. The mechanism was tuned for direction of motion. The data are discussed with reference to two alternative integration mechanisms: a low-level detector that is elongated in the direction of motion and a higher level integration mechanism characterized by cooperative or facilitatory interactions between low-level detectors tuned to the same direction of motion. Our data are consistent with a second-level, direction-specific process that integrates the responses of low-level motion detectors.     

Motion perception in the ageing visual system: minimum motion, motion coherence, and speed discrimination thresholds

We aimed to address two issues: first, to describe how the perception of motion differs in elderly observers as compared to younger ones; and, second, to see if these changes in motion perception could be accounted for by the known changes in the ability of elderly observers to detect patterns (as indexed via contrast sensitivity). The lower threshold of motion, motion coherence, and speed discrimination were measured, alongside contrast sensitivity, in a group of thirty-two older (mean age 61.5 years) and thirty-two younger (mean age 23.2 years) subjects. The older observers showed losses in their ability to detect slow motions as indexed via the lower threshold of motion for random-dot patterns and for gratings of a range of spatial frequencies. They also were impaired on a test of motion coherence, but only for stimuli of a slow to medium speed, whereas faster speeds showed no decline with age. Finally, at all speeds tested the older observers required greater differences in speed in order to discriminate between patterns moving at different speeds. The pattern of losses on motion perception tasks was not predicted by the deficits of the older groups, such as loss of detection thresholds for high spatial and/or temporal frequencies. It is concluded that these hypotheses do not provide an adequate account of the data, and therefore that the losses occurring with age are complex and probably are a result of the loss of several types of cell.     

Discriminating direction of motion trajectories from angular speed and background information

The effects of a background scene on the perception of the trajectory of an approaching object and its relation to changes in angular speed and angular size were examined in five experiments. Observers judged the direction (upward or downward) of two sequentially presented motion trajectories simulating a sphere traveling toward the observer at a constant 3-D speed from a fixed distance. In Experiments 1–4, we examined the effects of changes in angular speed and the presence of a scene background, with changes in angular size based either on the trajectories being discriminated or on an intermediate trajectory. In Experiment 5, we examined the effects of changes in angular speed and scene background, with angular size either constant or consistent with an intermediate 3-D trajectory. Overall, we found that (1) observers were able to judge the direction of object motion trajectories from angular speed changes; (2) observers were more accurate with a 3-D scene background, as compared with a uniform background, suggesting that scene information is important for recovering object motion trajectories; and (3) observers were more accurate in judging motion trajectories based on angular speed when the angular size function was consistent with motion in depth than when the angular size was constant.     

Negative emotionality influences the effects of emotion on time perception

In this study I used a temporal bisection task to test if greater overestimation of time due to negative emotion is moderated by individual differences in negative emotionality. The effects of fearful facial expressions on time perception were also examined. After a training phase, participants estimated the duration of facial expressions (anger, happiness, fearfulness) and a neutral-baseline facial expression. In accordance to the operation of an arousal-based process, the duration of angry expressions was consistently overestimated relative to other expressions and the baseline condition. In support of a role for individual differences in negative emotionality on time perception, temporal bias due to angry and fearful expressions was positively correlated to individual differences in self-reported negative emotionality. The results are discussed in relation both to the literature on attentional bias to facial expressions in anxiety and fearfulness and also, to the hypothesis that angry expressions evoke a fear-specific response.     

Contextual influences on interpersonal complementarity

The influence of context on interpersonal complementarity was examined using an event-contingent recording procedure. Setting and role status moderated the relation between how a person behaved and how the other person behaved. Individuals were more likely to respond with agreeable behavior to agreeableness in others when not at work than when at work and when in a high status work role relative to a low status work role. Reciprocity between dominance and submissiveness was found in work settings but not in nonwork settings. Individuals were more likely to reciprocate more submissive behavior by the other person with more dominant behavior and more likely to reciprocate more dominant behavior by the other person with relatively more submissive behavior when in a higher status work role relative to lower status work roles. Results were interpreted in terms of the influence of decreased structure and shared goals on increasing interpersonal complementarity.     

Driving speed changes and subjective estimates of time savings,accident risks and braking

Participants made decisions between two road improvements to increase mean speed. Time saved when speed increased from a higher driving speed was overestimated in relation to time saved from increases from lower speeds. In Study 2, participants matched pairs of speed increases so that they would give the same time saving and repeated the bias. The increase in risk of an accident with person injury was underestimated and the increase in risk of a fatal accident grossly underestimated when speed increased. The increase of stopping distance when speed increased was systematically underestimated. In Study 3, the tasks and results of Study 2 were repeated with engineering students. When forming opinions about speed limits and traffic planning, drivers, the public, politicians and others who do not collect the proper facts are liable to the same biases as those demonstrated in the present study. Copyright © 2008 John Wiley & Sons, Ltd.     

The perception of tactile distance: influences of body site, space, and time

Vibrotactile prostheses for deaf or blind persons have been applied to any number of different locations on the body, including the finger, wrist, forearm, abdomen, back, and nape of the neck. The discriminability of patterns presented by such devices can be affected by the acuity of the site of application and the resolution of the display. In addition, the mutual influences among stimuli close together in both space and time can affect percepts within a broad range of parameters. For example, consideration must be given to a variety of tactile illusions often associated with the spatial separations and the range of temporal intervals typically used in cutaneous communication displays. Experiments are reported in which magnitude estimates and cross-modality matches of perceived extent produced by pairs of vibrotactile taps presented to separate loci were obtained on three different body sites. Perceived distance was directly related both to the timing between the taps and to their physical separation. The findings show a consistent relationship to cortical magnification across body sites.     

Contrasting accounts of direction and shape perception in short-range motion: Counterchange compared with motion energy detection

It has long been thought (e.g., Cavanagh & Mather, 1989) that first-order motion-energy extraction via space-time comparator-type models (e.g., the elaborated Reichardt detector) is sufficient to account for human performance in the short-range motion paradigm (Braddick, 1974), including the perception of reverse-phi motion when the luminance polarity of the visual elements is inverted during successive frames. Human observers’ ability to discriminate motion direction and use coherent motion information to segregate a region of a random cinematogram and determine its shape was tested; they performed better in the same-, as compared with the inverted-, polarity condition. Computational analyses of short-range motion perception based on the elaborated Reichardt motion energy detector (van Santen & Sperling, 1985) predict, incorrectly, that symmetrical results will be obtained for the same- and inverted-polarity conditions. In contrast, the counterchange detector (Hock, Schöner, & Gilroy, 2009) predicts an asymmetry quite similar to that of human observers in both motion direction and shape discrimination. The further advantage of counterchange, as compared with motion energy, detection for the perception of spatial shape- and depth-from-motion is discussed.     

Contextual control of letter perception

This study examined the hypothesis that the type of list context in which a given item is embedded may affect the way in which it is perceptually processed. In the first experiment, subjects matched four types of test items inserted in four types of lists. The types of test items and the types of lists in which they were embedded were two-letter words, two-letter spelling clusters, unrelated letter pairs, and pairs of novel letters. The first experiment indicated that only unrelated letter pairs were significantly affected by type of list in which they were inserted. The pattern of the effect was confirmed in the latency data of the second experiment and the interpretation was that only unrelated letter and related letter-group contexts were operating in the first two experiments. The third and fourth experiments were concerned with contrasting contexts at the feature and letter levels of processing. By using lists in which type of catch trial either emphasized local features or global aspects of a pattern, the processing times of both familiar and unfamiliar letters were affected. The results of these experiments suggest that information processing models should incorporate structures which represent the way that context selectively facilitates processing of items at particular levels.     

Contextual influences on the sequential congruency effect

The sequential congruency effect (SCE) refers to the reduction in the size of the congruency effect following incongruent, relative to congruent, trials. Prior evidence indicated that the SCE does not generalize across tasks or different conflict-producing feature dimensions. We present results from a Stroop task showing that when the local list context is such that all colors and words appear in the same proportion of congruent trials, the SCE is present, but when those same items vary in the proportions congruent, the SCE is absent. We suggest that if stimuli are sufficiently consistent in the informativeness of their dimensions for the responses, individuals will attempt to track such information and weight the dimensions accordingly. In this way, the SCE reflects sequential adjustments to the weights given to individual stimulus dimensions in an attempt to track this information.     

Action, arousal, and subjective time

Saccadic chronostasis refers to the subjective temporal lengthening of the first visual stimulus perceived after an eye movement. It has been quantified using a duration discrimination task. Most models of human duration discrimination hypothesise an internal clock. These models could explain chronostasis as a transient increase in internal clock speed due to arousal following a saccade, leading to temporal overestimation. Two experiments are described which addressed this hypothesis by parametrically varying the duration of the stimuli that are being judged. Changes in internal clock speed predict chronostasis effects proportional to stimulus duration. No evidence for proportionality was found. Two further experiments assessed the appropriateness of the control conditions employed. Results indicated that the chronostasis effect is constant across a wide range of stimulus durations and does not reflect the pattern of visual stimulation experienced during a saccade, suggesting that arousal is not critical. Instead, alternative processes, such as one affecting the onset of timing (i.e., the time of internal clock switch closure) are implicated. Further research is required to select between these alternatives.     

A model of the influence of processing effort and number of changes on subjective time perception

The paper is concerned with a model for subjective time estimation as determined by processing effort and number of changes. In a previous paper, a proposal was made that should solve a problem of confounded variables in the area of time estimation. An experimental design was developed to allow for the independent manipulation of processing effort and number of changes. It is shown that this proposal is valid only under the assumption that Stevens' law holds with exponent one. Therefore, another way of conceptualizing this problem is advanced in which one asks for the relative impact of processing effort and change on the parameters of Stevens' law. It can be demonstrated that this law yields considerable fit despite interindividual differences.     

Contextual influences on interactive processing: Effects of discriminability,quantity, and uncertainty

Three contextual factors—(1) the discriminability of stimuli in pitch, (2) the number of stimuli differing in pitch, and (3)the uncertainty regarding which stimuli or tasks would appear—were manipulated as subjects performed speeded loudness classifications in each of six experiments. The magnitude of Garner interference and effects of congruity were used to gauge the degree of interactive processing. Enhancing pitch discriminability caused monotonic increases in interference and congruity. Stimulus-task uncertainty mediated the changes in Garner interference wrought by increased discriminability. Uncertainty also caused a surprising shift in congruity from strongly positive to strongly negative as uncertainty grew. Increasing stimulus quantity lowered interference, but had inconsistent effects on congruity. Regression analyses suggested that, collectively, these three contextual variables underlie most failures of selective attention in speeded classification.