Parallel ocular and manual tracking responses to a continuously moving visual target

Continuous ocular and manual tracking of the same visual target moving horizontally in sinusoids at 0.75 Hz was measured by lag, RMS Error, and Gain. The best measures of accuracy of tracking, error and lag, were remarkably similar in the two systems and were affected similarly by presence of a background and changes in predictability of target movement. Details of within-system performance varied despite the over-all parallels. Gain was different in adjustment of proportion of saccadic to pursuit movement was affected by the presence of the hand, even though this did not affect tracking accuracy. The over-all parallel of response adjustment suggests that a suprasystem decision-maker sets general response goals and each motor system adjusts output details to match these goals.     

Harming and failing to benefit: a reply to purves

Philosophical Studies - A prominent objection to the counterfactual comparative account of harm is that it classifies as harmful some events that are, intuitively, mere failures to benefit. In an...     

Predictive pointing movements and saccades toward a moving target

The authors investigated whether and, if so, how velocity information is used to control predictive manual pointing movements and saccades. Participants (N = 6) intercepted an occluded moving target as if it were still visible. They kept their eyes fixated while the target moved. The target traveled over a fixed distance and changed its velocity on the way. The presentation time of the final velocity was varied. Both the eye and the hand overshot the slow target and undershot the fast target, particularly when the duration of the final velocity was short. Thus, responses were biased in the direction of the target's initial velocity. The error seemed to arise because participants did not take their latency into account when aiming at the target. Instead, they strategically aimed farther ahead when the target was fast. Amplitude was also more related to the position of velocity change than to final velocity duration. Both findings suggest that target velocity is not extrapolated but that individuals add an increment to the position of velocity change.     

Playing it by ear: gregarious sparrows recognize and respond to isolated wingbeat sounds and predator-based cues

Animal Cognition - The ability to detect an incoming attack provides a final opportunity for an animal to avoid predation. In birds, vision is the main sensory mode in detecting attacks, but...     

Predicting the future position of a moving target

Three experiments were conducted to examine the processes underlying the prediction of the future position of a moving target. A target moved horizontally across a computer screen at constant velocity, disappearing partway across the screen, and subjects responded when they estimated the target would have passed a point on the far side of the screen, had it continued on its path. The first experiment demonstrated that visual tracking of the target is not necessary for successful position estimation. In the second experiment, the time over which the prediction was made rather than the interval for which the target was visible, the distance over which the prediction was made, or the velocity of the target, was found to affect performance. Finally, performance was not affected when markers were placed parallel to the trajectory of the target; the presence of gratings which masked portions of the target's path did not affect subjects' performance. The previous literature suggests that the spatial interval over which predictions are made is the important variable; we find that temporal factors are the major determinants of prediction.     

Stimulus control of the pigeon's ability to peck a moving target.

Two pigeons were trained to peck whichever of eight keys displayed a white field (SD). The other seven keys displayed a white "X" on a black background (S delta). Each peck to SD produced three-second access to grain, a three-second intertrial interval (ITI), and the next trial. Pecks to S delta produced a three-second timeout (TO) and the same trial. During later sessions the key displaying SD changed every t seconds (t = 3, 2, 1, .5, and .25 sec), requiring the birds to track the position of the SD. Pecks on a ninth key increased t. Several sessions employed novel stimuli to ascertain the controlling stimulus dimensions. Both birds made few errors acquiring the original discrimination. During the tracking sessions, both birds made few errors when t = .5 sec. Only one reliably lengthened t. Data from sessions with novel stimuli indicate that color and form were important aspects of SD and S delta respectively; movement contributed to the final performance.     

Visual search for a motion singleton among coherently moving distractors

In the current study, we tested whether search for a visual motion singleton presented among several coherently moving distractors can be more efficient than search for a motion stimulus presented with a single distractor. Under a variety of conditions, multiple spatially distributed and coherently moving distractors facilitated search for a uniquely moving target relative to a single-motion-distractor condition (Experiments 1, 3, and 4). Color coherencies among static distractors were not equally effective (Experiments 1 and 2). These results confirm that humans are highly sensitive to antagonistically directed motion signals in backgrounds compared with spatially more confined regions of visual images.     

Visual guidance of intercepting a moving target on foot

How do people walk to a moving target, and what visual information do they use to do so? Under a pursuit strategy, one would head toward the target's current position, whereas under an interception strategy, one would lead the target, ideally by maintaining a constant target-heading angle (or constant bearing angle). Either strategy may be guided by the egocentric direction of the target, local optic flow from the target, or global optic flow from the background. In four experiments, participants walked through a virtual environment to reach a target moving at a constant velocity. Regardless of the initial conditions, they walked ahead of the target for most of a trial at a fairly constant speed, consistent with an interception strategy (experiment 1). This behavior can be explained by trying to maintain a constant target-heading angle while trying to walk a straight path, with transient steering dynamics. In contrast to previous results for stationary targets, manipulation of the local optic flow from the target (experiment 2) and the global optic flow of the background (experiments 3 and 4) failed to influence interception behavior. Relative motion between the target and the background did affect the path slightly, presumably owing to its effect on perceived target motion. We conclude that humans use an interception strategy based on the egocentric direction of a moving target.     

Comparing target detection errors in visual search and manually-assisted search

Subjects searched for low- or high-prevalence targets among static nonoverlapping items or items piled in heaps that could be moved using a computer mouse. We replicated the classical prevalence effect both in visual search and when unpacking items from heaps, with more target misses under low prevalence. Moreover, we replicated our previous finding that while unpacking, people often move the target item without noticing (the unpacking error) and determined that these errors also increase under low prevalence. On the basis of a comparison of item movements during the manually-assisted search and eye movements during static visual search, we suggest that low prevalence leads to broadly reduced diligence during search but that the locus of this reduced diligence depends on the nature of the task. In particular, while misses during visual search often arise from a failure to inspect all of the items, misses during manually-assisted search more often result from a failure to adequately inspect individual items. Indeed, during manually-assisted search, over 90 % of target misses occurred despite subjects having moved the target item during search.     

Hitting a moving target: perception and action in the timing of rapid interceptions

Different interceptive tasks and modes of interception (hitting or capturing) do not necessarily involve similar control processes. Control based on preprogramming of movement parameters is possible for actions with brief movement times but is now widely rejected; continuous perceptuomotor control models are preferred for all types of interception. The rejection of preprogrammed control and acceptance of continuous control is evaluated for the timing of rapidly executed, manual hitting actions. It is shown that a preprogrammed control model is capable of providing a convincing account of observed behavior patterns that avoids many of the arguments that have been raised against it. Prominent continuous perceptual control models are analyzed within a common framework and are shown to be interpretable as feedback control strategies. Although these models can explain observations of on-line adjustments to movement, they offer only post hoc explanations for observed behavior patterns in hitting tasks and are not directly supported by data. It is proposed that rapid manual hitting tasks make up a class of interceptions for which a preprogrammed strategy is adopted--a strategy that minimizes the role of visual feedback. Such a strategy is effective when the task demands a high degree of temporal accuracy.     

Absence of attentional capture in parallel search is possible: A failure to replicate attentional capture in a non-singleton target search task

The notion of a singleton versus a feature search mode (Bacon & Egeth, 1994) in visual search is generally widely accepted. Yet Theeuwes (2004) claimed a different, potentially more parsimonious position. He suggested that the size of an attentional window is under top-down control and that salient distractors within this window capture attention. We report on four experiments. The first two experiments represent our various initial attempts to replicate the crucial Experiment 1 in the Theeuwes (2004) study, all of which were not successful. In Experiment 3, we showed that our distractor was able to yield attentional capture in a situation promoting the use of the singleton search mode (Bacon & Egeth, 1994). Experiment 4 was similar to Experiment 1 but incorporated further details that may account for the discrepant findings. Still, no attentional capture was found. In sum, it was not possible to replicate a crucial piece of evidence for the attentional window hypothesis, and our results are more consistent with the assumption of two different search modes.     

Dynamic visual capture: apparent auditory motion induced by a moving visual target

Apparent motion of a sound source can be induced by a moving visual target. The direction of the perceived motion of the sound source is the same as that of the visual target, but the subjective velocity of the sound source is 25-50% of that of the visual target measured under the same conditions. Eye tracking of the light target tends to enhance the apparent motion of the sound, but is not a prerequisite for its occurrence. The findings are discussed in connection with the 'visual capture' or 'ventriloquism' effect.     

Perception of initial moving target signals: support for a cumulative lateral inhibition theory

The cumulative lateral inhibition (CLI) theory of the Fr?hlich effect (perceptual mislocalization of the starting position of a moving target in the direction of movement) proposes that the target is difficult to see early in its trajectory because inhibitory feedback from later target views weakens initial target representations. In contrast, attention shift explanations contend that a phenomenal representation of the target is unavailable until attention has shifted to the vicinity of the target. Experiments 1-3 demonstrated that instructing naive undergraduate participants to accept different degrees of target clarity before making their response can alter the magnitude (and presence) of the Fr?hlich effect. Experiments 2-4 showed that increasing movement distance by adding target presentations reduced the visibility of the target at early positions. These results are difficult to reconcile with an attention shift account.     

Contextual cost: When a visual-search target is not where it should be

Visual search is often facilitated when the search display occasionally repeats, revealing a contextual-cueing effect. According to the associative-learning account, contextual cueing arises from associating the display configuration with the target location. However, recent findings emphasizing the importance of local context near the target have given rise to the possibility that low-level repetition priming may account for the contextual-cueing effect. This study distinguishes associative learning from local repetition priming by testing whether search is directed toward a target's expected location, even when the target is relocated. After participants searched for a T among Ls in displays that repeated 24 times, they completed a transfer session where the target was relocated locally to a previously blank location (Experiment 1) or to an adjacent distractor location (Experiment 2). Results revealed that contextual cueing decreased as the target appeared farther away from its expected location, ultimately resulting in a contextual cost when the target swapped locations with a local distractor. We conclude that target predictability is a key factor in contextual cueing.     

Age differences in visual search: target and distractor learning.

Age differences in a semantic category visual search task were investigated to determine whether the age effects were due to target learning deficits, distractor learning deficits, or a combination thereof. Twelve young (mean age 20) and 12 older (mean age 70) adults received 2,400 trials each in consistent and varied versions of the search task. Following training, a series of transfer-reversal manipulations allowed the assessment of target learning and distractor learning both in isolation and in combination. The pattern of data suggests that older adults have a deficit in their ability to increase the attention-attraction strength of targets and to decrease the attention-attraction strength of distractors. The results are interpreted in terms of a strength-based framework of visual search performance.     

Spatio-temporal constraints on upright children's coordination when hitting a moving target

To determine if the spatial and/or temporal context affected the coordination patterns of children under five in upright interceptive tasks, 3-year-olds hit a ball dropped from a ramp from five heights (1.5, 2, 2.5, 3, and 3.5 m) to control drop time. We studied the initiation time of hitting a ball with a cinematic analysis of the different joint movements (foot, knee, hip, shoulder, and hand). Two patterns of joint coordination were observed according to the rolling height of the ball: a de-synchronized pattern for heights of 2 m or above where the foot was the first to move and the hand the last, and a “synchronized” pattern, for the lowest height (1.5 m) where all joints started moving at the same time due to a strong temporal pressure. These two coordination patterns highlight a functional adaptation of body joints according to the spatio-temporal constraints among children from the age of three.     

The role of configuration and target discriminability in a visual search task

Ss sorted through decks of cards bearing five-element patterns, separating those in which all five were identical from those in which one of the five was different from the remaining four. Sorting time depended on the configuration and size of the pattern in which the elements were arranged but was independent of the goodness of these patterns. It was concluded that Ss did not attend to the patterns themselves, but just to the elements comprising them in searching for the discrepant element. The differences owing to the patterns appear to be due in part to the compactness of the configurations.     

The target effect: Visual memory for unnamed search targets

Search targets are typically remembered much better than other objects even when they are viewed for less time. However, targets have two advantages that other objects in search displays do not have: They are identified categorically before the search, and finding them represents the goal of the search task. The current research investigated the contributions of both of these types of information to the long-term visual memory representations of search targets. Participants completed either a predefined search or a unique-object search in which targets were not defined with specific categorical labels before searching. Subsequent memory results indicated that search target memory was better than distractor memory even following ambiguously defined searches and when the distractors were viewed significantly longer. Superior target memory appears to result from a qualitatively different representation from those of distractor objects, indicating that decision processes influence visual memory.