Separate motion-detecting mechanisms for first- and second-order patterns revealed by rapid forms of visual motion priming and motion aftereffect (original) (raw)
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Position displacement, not velocity, is the cue to motion detection of second-order stimuli
1998
Motion detection can be achieved either with mechanisms sensitive to a target's velocity, or sensitive to change in a target's position. Using a procedure to dissociate these two provided by Nakayama and Tyler (Vis Res 1981;21:427 -433), we explored detection of first-order (luminance-based) and various second-order (texture-based and stereo-based) motion. In the first experiment, observers viewed annular gratings oscillating in rotational motion at various rates. For each oscillation temporal frequency, we determined the minimum displacement of the pattern for which observers could reliably see motion. For first-order motion, these motion detection thresholds decreased with increasing temporal frequency, and thus were determined by a minimum velocity. In contrast, motion detection thresholds for second-order motion remained roughly constant across temporal frequency, and thus were determined by a minimum displacement. In Experiment 2, luminance-based gratings of different contrasts were tested to show that the velocity-dependence was not an artifact of pattern visibility. In the remaining experiments, results similar to Experiment 1 were obtained with a central presentation of a linear grating, instead of an annular grating (Experiment 3), and with a motion discrimination (phase discrimination) rather than motion detection task (Experiment 4). We conclude that, within the ranges tested here, second-order motion is more readily detected with a mechanism which tracks the change of position of features over time.
Adaptation to motion of a second-order pattern: the motion aftereffect is not a general result
Vision Research, 1997
It has become apparent from recent work that the spatial frequency and orientation content of the first-order (luminance) carrier is very important in determining the properties of a second-order (contrast) modulation of that carrier. In light of this we examined whether there was any evidence for a motion aftereffect in one-dimensional second-order patterns containing only two sinusoidal luminance components: a spatial beat. The stimuli were either I cpd luminance sinusoids or I cpd luminance beats modulating a carrier sinusoid of 5 cpd. The magnitude of any motion aftereffect, or any directionally specific effect of adaptation, was measured for all combinations of first and second-order test and adapting patterns. Both flickering and non-flickering stimuli were used. The results indicate that a motion aftereffect is only induced by first-order adapting stimuli, and likewise, is only measurable in first-order test stimuli. We find no evidence for any directionally specific effect of adaptation in second-order stimuli, whether the test is counterphased or otherwise. These results apparently conflict with recent reports of a second-order induced motion aftereffect, but are consistent with many other findings which show differences between the detection of motion for first and second-order stimuli. We conclude that the induction of a motion aftereffect for second-order stimuli is not a general result and is critically dependent upon (amongst other things) the local properties of the stimulus, including the spatial frequency and orientation content of the first-order carrier.
A common mechanism for the perception of first-order and second-order apparent motion
Vision Research, 2005
A common mechanism for perceiving first-order, luminance-defined, and second-order, texture-contrast defined apparent motion between two element locations is indicated by: (1) transitivity-whether or not motion is perceived is interchangeably affected by activationally equivalent luminance and contrast changes at each location, (2) local integration-whether or not motion is perceived depends on the net activation change resulting from simultaneous background-relative luminance and background-relative contrast changes at the same element location, and (3) inseparability-apparent motion is not perceived through independent first-or second-order mechanisms when luminance and contrast co-vary at the same location. These results, which are predicted by the response characteristics of directionally selective cells in areas V1, MT, and MST, are not instead attributable to changes in the location of the most salient element (third-order motion), attentive feature tracking, or artifactual first-order motion. Their inconsistency with Lu and SperlingÕs [Lu, Z., Sperling, G. (1995a). Attention-generated apparent motion. Nature 377, 237, Lu, Z., Sperling, G. (2001). Three-systems theory of human visual motion perception: review and update. Journal of the Optical Society of America A 18, 2331] model, which specifies independent first-and second-order mechanisms, may be due to computational requirements particular to the motion of discrete objects with distinct boundaries defined by spatial differences in luminance, texture contrast, or both.
The direction aftereffect is driven by adaptation of local motion detectors
The processing of motion information by the visual system can be decomposed into two general stages; point-by-point local motion extraction, followed by global motion extraction through the pooling of the local motion signals. The direction aftereffect (DAE) is a well known phenomenon in which prior adaptation to a unidirectional moving pattern results in an exaggerated perceived direction difference between the adapted direction and a subsequently viewed stimulus moving in a different direction. The experiments in this paper sought to identify where the adaptation underlying the DAE occurs within the motion processing hierarchy. We found that the DAE exhibits interocular transfer, thus demonstrating that the underlying adapted neural mechanisms are binocularly driven and must, therefore, reside in the visual cortex. The remaining experiments measured the speed tuning of the DAE, and used the derived function to test a number of local and global models of the phenomenon. Our data provide compelling evidence that the DAE is driven by the adaptation of motion-sensitive neurons at the local-processing stage of motion encoding. This is in contrast to earlier research showing that direction repulsion, which can be viewed as a simultaneous presentation counterpart to the DAE, is a global motion process. This leads us to conclude that the DAE and direction repulsion reflect interactions between motion-sensitive neural mechanisms at different levels of the motion-processing hierarchy.
Visual motion aftereffects arise from a cascade of two isomorphic adaptation mechanisms
Journal of Vision, 2009
Prolonged exposure to a moving stimulus can substantially alter the perceived velocity (both speed and direction) of subsequently presented stimuli. Here, we show that these changes can be parsimoniously explained with a model that combines the effects of two isomorphic adaptation mechanisms, one nondirectional and one directional. Each produces a pattern of velocity biases that serves as an observable "signature" of the corresponding mechanism. The net effect on perceived velocity is a superposition of these two signatures. By examining human velocity judgments in the context of different adaptor velocities, we are able to separate these two signatures. The model fits the data well, successfully predicts subjects' behavior in an additional experiment using a nondirectional adaptor, and is in agreement with a variety of previous experimental results. As such, the model provides a unifying explanation for the diversity of motion aftereffects.
Vision Research, 2005
Visual neurons show fast adaptive behavior in response to brief visual input. However, the perceptual consequences of this rapid neural adaptation are less known. Here, we show that brief exposure to a moving adaptation stimulus-ranging from tens to hundreds of milliseconds-influences the perception of a subsequently presented ambiguous motion test stimulus. Whether the ambiguous motion is perceived to move in the same direction (priming), or in the opposite direction (rapid motion aftereffect) varies systematically with the duration of the adaptation stimulus and the adaptation-test blank interval. These biases appear and decay rapidly. Moreover, when the adapting stimulus is itself ambiguous, these effects are not produced. Instead, the percept for the subsequent test stimulus is biased to the perceived direction of the adaptation stimulus. This effect (perceptual sensitization) builds gradually over the time between the adaptation and test stimuli. Our results indicate that rapid adaptation plays a role mainly within early motion processing, whereas a slow potentiation controls the sensitivity at a later stage.
Discriminating the direction of second-order motion at short stimulus durations
Vision Research, 1993
We measured the ability of human observers to discriminate the direction of motion of ditTerent spatial patterns presented for durations ranging from 0.021 to 0.67 sec. The patterns were: (1) a vertical grating (spatial frequency 0.93 c/deg at 5% contrast); (2) a "beat" pattern made by adding vertical gratings of 6.3 and 5.4 c/deg both at 5% contrast moving in opposite directions (this pattern appears as a horizontally moving, 0.93 c/deg "beat"; i.e. spatial variation in the contrast of a stationary vertical grating of 5.8 c/deg); and (3) a "plaid" pattern made by adding gratings of 5.9 c/deg orientated f 81 deg from vertical (this pattern can also be expressed as a horizontally moving 1.9 c/deg beat in a kizontal grating of 5.8 c/deg). The direction of motion of the grating and the plaid pattern were discrhninable at all durations tested. The direction of motion of the beat could only be discriminated at durations above approx. 200 msec. We suggest that this is a consequence of the fact that the moving beat is only visible to second-order mechanisms, and that second-order mechanisms for the analysis of motion operate more slowly than lfrsr -order mechanisms.
Visual motion aftereffects: Differential adaptation and test stimulation
Vision Research, 1998
The local motion adaptation at the basis of the motion aftereffect (MAE) can be expressed in a variety of ways, depending upon the structure of the test display [Wade et al. (1996). Vision Research, 36, 2167–2175]. Three experiments are reported, which examined the characteristics of the test display and of the local adaptation process. In Experiment 1, MAEs were recorded in the central of three test gratings but their directions depended on the location of the centre relative to the adapting gratings. The effects of adapting motions in different directions were examined in Experiments 2 and 3, in which one or two adapting gratings were presented above or above and below a fixation cross. The upper grating always received the same (leftward) direction of motion during adaptation, and the lower grating was: moving in the opposite direction, stationary, moving in the same direction, or absent. The results indicate that no MAE is visible in the upper grating when a single test grating is observed (Experiment 2) and only occurs with two test gratings following differential adaptation between the upper and lower gratings (Experiment 3). Thus, the MAE occurs as a consequence of adapting restricted retinal regions to motion but it can only be expressed when differentially adapted regions are also tested.
Vision Research, 2003
Previous studies [e.g. Vision Research 40 (2000) 173] have shown that when observers are required to selectively attend to one of two, spatially-adjacent patches containing either first-order (luminance-defined) or second-order (contrast-defined) motion, threshold sensitivity for identifying the direction of second-order motion, but not first-order motion, is enhanced for the attended stimuli. The processing of second-order motion, unlike first-order motion, may, therefore, require attention. However, other studies have found little evidence for differential effects of attention on the processing of first-order and second-order motion [Investigative Ophthalmology and Visual Science 42 ]. We investigated the effects of attention instructions on the ability of observers to identify the directions and spatial orientations of luminance-defined and contrast-defined motion stimuli. Pairs of motion stimuli were presented simultaneously and threshold performance was measured over a wide range of drift temporal frequencies and stimulus durations. We found: (1) direction discrimination thresholds for attended motion stimuli were lower than those for unattended stimuli for both types of motion. The magnitude of this effect was reduced when the observers were not given prior knowledge of which patch of motion (attended or unattended) they had to judge first. (2) Direction discrimination for first-order motion was similarly affected at all temporal frequencies and durations examined, but for second-order motion the effects of attention depended critically on the drift temporal frequency and stimulus duration used. (3) Orientation discrimination showed little or no influence of attention instructions. Thus, whether or not attention influences the processing of second-order motion depends crucially on the precise stimulus parameters tested. Furthermore under appropriate conditions the processing of first-order motion is also influenced by attention, albeit to a lesser extent than second-order motion.
Probing Visual Motion Signals with a Priming Paradigm
Vision Research, 1997
The perceived motion of a vertical sine-wave luminance grating which undergoes an abrupt 180 deg phase shift (motion step) is ambiguous. The grating sometimes appears to move rightward; sometimes Ieftward. However, when the 180 deg step follows closely upon an unambiguous grating step, the 180 deg step appears to be in the same direction as the unambiguous step. This phenomenon is termed visual motion priming (VMP), and some of the characteristics of the phenomenon were investigated in a series of experiments. The main findings were that priming (1) lasted for hundreds of msec; (2) was at a maximum when the magnitude of the priming step was 90 deg; (3) was scarcely affected by spatial frequency in the range 0.7-2.8 c/deg; and (4) at suprathreshold contrasts depended upon the relative contrast, not the absolute contrasts, of the frames comprising the priming step. The experiments were conducted within the framework of a motion energy model (Adelson & Bergen, 1985) which possessed an extra stage which summed motion signals over time. Some of the results could be explained by the second-stage integrator. Other nonlinear relationships between VMP and contrast require some form of motion signal compression, and perhaps even a mechanism of dynamic contrast processing.