200,928 research outputs found

    Effects of Motion Pattern Characteristics on the Perception of Visual Acceleration

    Get PDF
    The ability to perceive visual motion is one that we use every day to perform goal-directed activities, such as intercepting or avoiding objects. As objects and observers rarely move at constant velocities, it is important to be able to detect changes in velocity. However, little attention has been paid to how we perceive visual acceleration in the literature. This thesis explored the influence of real world-relevant motion pattern characteristics on visual acceleration perception. Observers rarely see object motion with an unlimited field of view, and therefore we first examined how physically constraining the horizontal distance over which a stimulus can move affects the ability to detect and pursue horizontal acceleration and deceleration at different average velocities. Results indicated that detection improves and smooth pursuit worsens as average velocity increases. Moreover, both improve as the horizontal aperture size increases. Given our asymmetrical experience with the frequency and relevance of upward compared to downward events due to gravity, we then investigated whether acceleration and deceleration detection vary as a function of vertical direction. We also tested whether the effects of aperture size on detection and pursuit persist on the vertical axis. Our data suggested that detection is better for downward than upward motion, and both detection and smooth pursuit improve as the vertical aperture size increases. Considering that we tend to see translation as well as more complex motion patterns outside the laboratory, we subsequently explored whether acceleration and deceleration detection vary between horizontal translation and radial optic flow, which is similar to the motion we see when moving forward or backward while looking straight ahead. We found that detection is better for radial than horizontal motion, although direction within each pattern type has no effect. Finally, we verified that sensitivity to the presence of acceleration is uniform across the optic flow field, regardless of radial direction. In summary, although we detect acceleration and deceleration similarly across a wide range of conditions, overall perception appears to be affected by the unique characteristics of the motion pattern

    Change blindness: eradication of gestalt strategies

    Get PDF
    Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

    Optic flow based perception of two-dimensional trajectories and the effects of a single landmark.

    Get PDF
    It is well established that human observers can detect their heading direction on a very short time scale on the basis of optic flow. Can they also integrate these perceptions over time to reconstruct a 2D trajectory simulated by the optic flow stimulus? We investigated the visual perception and reconstruction of visually travelled two-dimensional trajectories from optic flow with and without a single landmark. Stimuli in which translation and yaw are unyoked can give rise to illusory percepts; using a structured visual environment instead of only dots can improve perception of these stimuli. Does the additional visual and/or extra-retinal information provided by a single landmark have a similar, beneficial effect? Here, seated, stationary subjects wore a head-mounted display showing optic flow stimuli that simulated various manoeuvres: linear or curvilinear 2D trajectories over a horizontal plane. The simulated orientation was either fixed in space, fixed relative to the path, or changed relative to both. Afterwards, subjects reproduced the perceived manoeuvre with a model vehicle, of which we recorded position and orientation. Yaw was perceived correctly. Perception of the travelled path was less accurate, but still good when the simulated orientation was fixed in space or relative to the trajectory. When the amount of yaw was not equal to the rotation of the path, or in the opposite direction, subjects still perceived orientation as fixed relative to the trajectory. This caused trajectory misperception because yaw was wrongly attributed to a rotation of the path. A single landmark could improve perception

    Motion adaptation and attention: A critical review and meta-analysis

    Get PDF
    The motion aftereffect (MAE) provides a behavioural probe into the mechanisms underlying motion perception, and has been used to study the effects of attention on motion processing. Visual attention can enhance detection and discrimination of selected visual signals. However, the relationship between attention and motion processing remains contentious: not all studies find that attention increases MAEs. Our meta-analysis reveals several factors that explain superficially discrepant findings. Across studies (37 independent samples, 76 effects) motion adaptation was significantly and substantially enhanced by attention (Cohen's d = 1.12, p < .0001). The effect more than doubled when adapting to translating (vs. expanding or rotating) motion. Other factors affecting the attention-MAE relationship included stimulus size, eccentricity and speed. By considering these behavioural analyses alongside neurophysiological work, we conclude that feature-based (rather than spatial, or object-based) attention is the biggest driver of sensory adaptation. Comparisons between naïve and non-naïve observers, different response paradigms, and assessment of 'file-drawer effects' indicate that neither response bias nor publication bias are likely to have significantly inflated the estimated effect of attention

    The effect of pictorial depth information on projected size judgements

    Get PDF
    When full depth cues are available, size judgements are dominated by physical size. However, with reduced depth cues, size judgements are less influenced by physical size and more influenced by projected size. This study reduces depth cues further than previous size judgement studies, by manipulating monocularly presented pictorial depth cues only. Participants were monocularly presented with two shapes against a background of zero (control), one, two or three pictorial depth cues. Each cue was added progressively in the following order: height in the visual field, linear perspective, and texture gradient. Participants made a „same-different? judgement regarding the projected size of the two shapes, i.e. ignoring any depth cues. As expected, accuracy increased and response times decreased as the ratio between the projected size of the two shapes increased (range of projected size ratios, 1:1 to 1:5). In addition, with the exception of the larger size ratios (1:4 and 1:5), detection of projected size difference was poorer as depth cues were added. One-cue and two-cue conditions had the most weighting in this performance decrement, with little weighting from the three-cue condition. We conclude that even minimal depth information is difficult to inhibit. This indicates that depth perception requires little focussed attention
    • …
    corecore