Expanding and contracting optic-flow patterns and vection

When stationary observers view an optic-flow pattern, visually induced self-motion perception (vection) and a form of motion sickness known as simulator sickness (SS), can result. Previous results suggest that an expanding flow pattern leads to more SS than a contracting pattern. Sensory conflict, a possible cause of SS, may be more salient when an expanding optic-flow pattern is viewed. An experiment was conducted to test if a more salient sensory conflict accompanying expanding flow patterns might inhibit vection. Participants (n = 15) viewed a pattern of blue squares, either steadily expanded or contracted, on a large rear-projection screen. Vection onset and magnitude were measured for 30 s with a computer-interfaced slide device. Vection onset was significantly faster, and vection magnitude stronger, when a contracting pattern was viewed. We propose that our extensive experience with forward self-motion may form a neural expectancy (exposure-history) about the sensory inputs which typically accompany expanding flow. However, since backward self-motion is less common, there may be a weaker exposure-history for contracting flow, and as a result these patterns generate less salient sensory conflict and subsequently less vection.     

Complexity and goodness of dot patterns varying in symmetry

Summary Two experiments were performed to specify stimulus determinants of pattern complexity and pattern goodness. Dot patterns distributed in 3×3 and 4×4 matrices with a rectilinear frame were used in Experiment 1, and dot patterns in hexagonal frameworks with a circular frame were used in Experiment 2. The patterns were invariant for transformations of rotation or reflection, and formed symmetry groups of different orders, i.e., cyclic and dihedral groups. The complexity and goodness of the patterns depended upon such stimulus variables as follows: (1) complexity decreased with the order of symmetry groups with equal weights for cyclic and dihedral groups, whereas goodness increased with the order of both symmetry groups with different weights; (2) the simplicity and goodness of patterns with a vertical axis were greater than those with a horizontal axis and those with an oblique one; (3) the complexity of the patterns that had collinear elements with equal length was rated the simplest; (4) pattern goodness increased as a function of the number of dots and the concentrations of dot to rotation/reflection axis in 3×3 and 4 × 4 matrices. Thus, complexity and goodness of pattern differed with respect to these stimulus variables.     

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.     

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.     

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.     

Visuomotor rotations of varying size and direction compete for a single internal model in motor working memory

When participants adapt to equal and opposite visuomotor rotations in close temporal proximity, memory of the 1st is not consolidated. The authors investigated whether this retrograde interference depends on the use of equal and opposite rotations. On Day 1, different groups of participants adapted to a -30 degrees rotation followed 5 min later by rotations of +30 degrees, +60 degrees, or -60 degrees. On Day 2, all groups were retested on the -30 degrees rotation. Either retrograde interference (in groups who adapted to rotations of opposite sign on Day 1) or retrograde facilitation (in the remaining group) was observed. In all groups, learning of the 2nd rotation resulted in unlearning of the first, indicating that all visuomotor rotations compete for common working memory resources.     

Identification of interindividual and intraindividual movement patterns in handball players of varying expertise levels

The authors examined the movement patterns of 5 left-handed handball players (ranging from beginner to national level) who threw a handball to different sections of a goal as if a goalkeeper were present. The authors used time-continuous, 3-dimensional kinematic data to assess interindividual movement patterns and considered participants' intraindividual differences relative to different targets. Cluster analysis yielded the highest assignment rates for level of expertise; a mean of 92% of trials was correctly assessed. The authors observed an interaction with expertise for the intraindividual movement patterns. Variability in the novice throwers was increased, whereas (a) advanced throwers experienced a period of stability, and (b) the expert thrower's variability was increased. The results indicate that random variability characterizes novice motor performance, whereas active functional variability may exemplify expert motor performance.     

Categorizing a moving target in terms of its speed,direction, or both

Pigeons categorized a moving target in terms of its speed and direction in an adaptation of the randomization procedure used to study human categorization behavior (Ashby & Maddox, 1998). The target moved according to vectors that were sampled with equal probabilities from two slightly overlapping bivariate normal distributions with the dimensions of speed and direction. On the average, pigeons categorized optimally in that they attended to either speed or direction alone, or divided attention between them, as was required by different reinforcement contingencies. Decision bounds were estimated for individual pigeons for each attentional task. Average slopes and y intercepts of these individually estimated decision bounds closely approximated the corresponding values for optimal decision bounds. There is therefore at least one task in which pigeons, on the average, display flexibility and quantitative precision in allocating attention to speed and direction when they categorize moving targets.     

Perception of surface curvature and direction of illumination from patterns of shading

Three experiments examine the perceptual salience of shading information for the visual specification of three-dimensional form. The observers in these experiments were required to estimate the surface curvature and direction of illumination depicted in computer-synthesized images of cylindrical surfaces, both with and without texture. The results indicate that the shininess of a surface enhances the perception of curvature, but has no effect on perceived direction of illumination; and that shading is generally less effective than texture for depicting surfaces in three dimensions. These and other findings are used to evaluate the psychological validity of several mathematical analyses of shading information that have recently been proposed in the literature.     

Measuring individual differences in sensitivities to basic emotions in faces

The assessment of individual differences in facial expression recognition is normally required to address two major issues: (1) high agreement level (ceiling effect) and (2) differential difficulty levels across emotions. We propose a new assessment method designed to quantify individual differences in the recognition of the six basic emotions, 'sensitivities to basic emotions in faces.' We attempted to address the two major assessment issues by using morphing techniques and item response theory (IRT). We used morphing to create intermediate, mixed facial expression stimuli with various levels of recognition difficulty. Applying IRT enabled us to estimate the individual latent trait levels underlying the recognition of respective emotions (sensitivity scores), unbiased by stimulus properties that constitute difficulty. In a series of two experiments we demonstrated that the sensitivity scores successfully addressed the two major assessment issues and their concomitant individual variability. Intriguingly, correlational analyses of the sensitivity scores to different emotions produced orthogonality between happy and non-happy emotion recognition. To our knowledge, this is the first report of the independence of happiness recognition, unaffected by stimulus difficulty.     

Learning to vary and varying to learn

We compared two sources of behavior variability: decreased levels of reinforcement and reinforcement contingent on variability itself. In Experiment 1, four groups of rats were reinforced for different levels of response-sequence variability: one group was reinforced for low variability, two groups were reinforced for intermediate levels, and one group was reinforced for very high variability. All of the groups experienced three different reinforcement frequencies for meeting their respective variability contingencies. Results showed that reinforcement contingencies controlled response variability more than did reinforcement frequencies. Experiment 2 showed that only those animals concurrently reinforced for high variability acquired a difficult-to-learn sequence; animals reinforced for low variability learned little or not at all. Variability was therefore controlled mainly by reinforcement contingencies, and learning increased as a function of levels of baseline variability. Knowledge of these relationships may be helpful to those who attempt to condition operant responses.     

Contextual influences of dimension, speed, and direction of motion on subjective time perception

Research has indicated that the direction of motion and the speed of motion can influence the subjective estimates of temporal duration of two-dimensional (2-D) stimuli expanding and contracting within the picture plane. In this study, we investigated whether the contextual cues of stimulus/movement-plane dimensionality (2-D stimuli with implied movement in the picture plane or depth-rendered “3-D” stimuli with implied movement in the depth plane) influence and interact with speed and implied movement direction during interval estimation. Participants viewed a series of standard stimulus durations followed by a test stimulus duration and determined whether the test and standard durations differed. The results indicated that moving stimuli were overestimated relative to stationary stimuli, regardless of the direction of motion or dimensionality. Also, faster-moving stimuli were overestimated relative to slower-moving stimuli. Importantly, an interaction between movement direction and dimensional cues indicated that the loom/recede distinction occurs for 2-D but not for 3-D stimuli. It is possible that the loom/recede distinction for the 2-D condition may be an artifact arising from reduced or from a lack of perceived motion in 2-D “recede” conditions, rather than a specific overestimation for looming stimuli.     

The influence of speed and force on bimanual finger tapping patterns.

The current study investigated factors that affect the stability of anti-phase bimanual finger tapping. Past research employing the order parameter and control parameter concepts, has identified frequency of movement as a control parameter that affects the stability of finger movement patterns (the order parameter). The present study investigated the hypothesis that multiple movement related variables can interact to influence the stability of an order parameter. Specifically, the combined effect of the rate of movement and movement force on the stability of bimanual finger tapping was examined. Participants were required to initiate an anti-phase tapping pattern under three different movement rate conditions (600, 400, and 200 ms), and were required to increase the force of one finger at the onset of a randomly presented stimulus. The results indicate that an increase in the force parameter at lower tapping rates (600 ms) did not affect the phase relation of the fingers, however at higher rates (200 and 400 ms), the introduction of a force parameter resulted in fluctuations of the phase relation of the fingers, which were followed by pattern shifts from anti-phase to in-phase tapping. The results indicate that movement force and rate of movement interact to influence the outcome of the tapping pattern. Further research is required to investigate force as a control parameter.     

The combined influence of body weight support and running direction on self-selected movement patterns

We investigated metabolic costs, muscle activity, and perceptual responses during forward and backward running at matched speeds at different body weight support (BWS) conditions. Participants ran forward and backward on a lower body positive pressure treadmill at 0%BWS, 20%BWS, and 50%BWS conditions. We measured oxygen uptake, carbon dioxide production, heart rate, muscle activity, and stride frequency. Additionally, we calculated metabolic cost of transport. Furthermore, we used rating of perceived exertion and feeling scale to investigate perceptual responses. Feeling scale during running was higher with increasing BWS (0–50%BWS), regardless of running direction (p < 0.05). Oxygen uptake, heart rate, and metabolic cost of transport were influenced by the interaction of running direction and BWS (p < 0.01). For example, metabolic cost of transport during backward running was greater than when running forward only when running at 0%BWS (i.e., 4.4 ± 1.1 and 5.8 ± 1.4 J/kg/m for forward and backward running, respectively: p < 0.001). However, rectus femoris muscle activity, stride frequency, and rating of perceived exertion during backward running were averages of 113.5%, 11.3%, and 2.8 rankings greater than when running forward, respectively, regardless of BWS (p < 0.001). We interpret our observations to indicate that environment (in the context of effective body weight) is a critical factor that determines self-selected movement patterns during forward and backward running.     

The relative sensitivities of same-different and identification judgment models to perceptual dependence

Probabilistic models of same-different and identification judgments are compared (within each paradigm) with regard to their sensitivity to perceptual dependence or the degree to which the underlying psychological dimensions are correlated. Three same-different judgment models are compared. One is a step function or decision bound model and the other two are probabilistic variants of a similarity model proposed by Shepard. Three types of identification models are compared: decision bound models, a probabilistic multidimensional scaling model, and probabilistic models based on the Shepard-Luce choice rule. The decision bound models were found to be most sensitive to perceptual dependence, especially when there is considerable distributional overlap. The same-different model based on the city-block metric and an exponential decay similarity function, and the corresponding identification model were found to be particularly insensitive to perceptual dependence. These results suggest that if a Shepard-type similarity function accurately describes behavior, then under typical experimental conditions it should be difficult to see the effects of perceptual dependence. This result provides strong support for a perceptualindependence assumption when using these models. These theoretical results may also play an important role in studying different decision rules employed at different stages of identification training.We thank Robert Melara, Jerome Busemeyer and three anonymous reviewers for comments on an earlier draft of this paper.