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ABSTRACT: Duncker (1929/1955, Source Book of Gestalt Psychology, pp 161-172) demonstrated a laboratory version of induced motion. He showed that, when a stationary spot of light in a dark laboratory is enclosed in an oscillating rectangular frame, the frame is perceived as stationary and the dot appears to move in the direction opposite the true motion of the frame. Zivotofsky (2004, Investigative Ophthalmology & Visual Science 45 2867-2872) studied a more complex variant of the Duncker illusion, in which both the inducing and the test stimuli moved: a single red test dot moved horizontally left or right while a dense background set of black dots on a white background moved vertically up or down. When the background inducing dots moved up (down), the truly horizontally translating test dot appeared to drift at an angle down (up) from the horizontal. In experiment 1, we used two methods to measure the complete angular function of the Zivotofsky effect and found it to peak with an inducer-test direction separation of approximately 30 degrees, similar to the inducing angle that has been found to maximise other direction illusions. Experiment 2 tested and confirmed predictions regarding the effects of relative test and inducer speeds based on the vectorial subtraction of the inducing velocity from the test velocity.
Perception 01/2012; 41(6):733-46. · 1.31 Impact Factor
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ABSTRACT: In order to investigate the relationship between 'neural speedlines', form (shape), and fast motion-direction decisions, Glass patterns were constructed with dipoles assuming a tapered shape. The results of a 2-alternative forced-choice direction-discrimination task, for both concentric and translational Glass-pattern sequences, suggest that with short stimulus presentations (< 1 s) form can influence direction decisions. This result implies that neural speedlines may be analogous to tapered lines and further supports Geisler's (1999, Nature 400 65-69) model of form/motion interaction.
Perception 01/2011; 40(4):383-91. · 1.31 Impact Factor
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ABSTRACT: Simultaneous direction repulsion (the direction illusion) occurs in bidirectional motion displays, typically transparent motion random dot kinematograms. Several laboratories have reported a greatly reduced illusion with dichoptic presentation of the two coherently translating stimuli as compared to monocular or binocular presentation. Some researchers have argued that those results might be due to a confounding factor, namely binocular rivalry occurring between test and inducing stimuli in the dichoptic condition, and so have attributed decisive weight to the results reported by Kim and Wilson (1997, Vision Research, 37, 991-1005) who used centre-surround grating stimuli and found large monocular as well as large dichoptic effects. Here we use centre-surround dot stimuli - with which no binocular rivalry occurs - to confirm a strong monocular contribution to the direction illusion. In addition, we fail to find evidence of a direction illusion with centre-surround grating stimuli, even when seeking to replicate the methods of Kim and Wilson (1997). In light of other evidence that a global motion-sensitive mechanism can determine the magnitude of the direction illusion, we propose that simultaneous direction repulsion can result from activity at multiple stages of the motion processing hierarchy.
Vision research 08/2010; 50(18):1824-32. · 2.29 Impact Factor
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ABSTRACT: We studied binocular rivalry between orthogonally translating arrays of random Gaussian blobs and measured the strength of rivalry suppression for static oriented probes. Suppression depth was quantified by expressing monocular probe thresholds during dominance relative to thresholds during suppression. Rivalry between two fast motions or two slow motions was compared in order to test the suggestion that fast-moving objects leave oriented "motion streaks" due to temporal integration (W. S. Geisler, 1999). If fast motions do produce motion streaks, then fast motion rivalry might also entail rivalry between the orthogonal streak orientations. We tested this using a static oriented probe that was aligned either parallel to the motion trajectory (hence collinear with the "streaks") or was orthogonal to the trajectory, predicting that rivalry suppression would be greater for parallel probes, and only for rivalry between fast motions. Results confirmed that suppression depth did depend on probe orientation for fast motion but not for slow motion. Further experiments showed that threshold elevations for the oriented probe during suppression exhibited clear orientation tuning. However, orientation-tuned elevations were also present during dominance, suggesting within-channel masking as the basis of the extra-deep suppression. In sum, the presence of orientation-dependent suppression in fast motion rivalry is consistent with the "motion streaks" hypothesis.
Journal of Vision 01/2009; 9(5):10.1-14. · 3.38 Impact Factor
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ABSTRACT: Adding an upright inner square frame to an outer tilted square frame causes a central rod's perceived orientation to be directionally opposite the usual rod-and-frame illusion (RFI). Zoccolotti, Antonucci, Daini, Martelli, and Spinelli (1997) attributed this double RFI (DRFI) to Rock's (1990) hierarchical organization principle. In Experiment 1, this explanation predicted results for small (11 degrees ) but not larger (22 degrees and 33 degrees ) outer frame orientations. In two experiments with the DRFI, bottom-up, goal-driven attention was varied and direct and indirect measures of the framework's influence were compared. In Experiment 2, the RFI angular function was compared with two other DRFI conditions: a direct measure of perceived rod orientation and an indirect measure of the inner frame. These conditions induced directionally opposite effects. In Experiment 3, direct and indirect measures of the inner frame's perceived tilt were compared. Angular functions differing in size and direction were obtained. Experiment 4 replicated the previous results, using a different psychophysical procedure. All the results were consistent with the hierarchical organization mechanism but suggested different processing strategies due to different attentional weights. They were also consistent with other recent findings based on the Bayesian approach to accounts of illusory phenomena (e.g., Jazayeri & Movshon, 2006, 2007; Weiss, Simoncelli, & Adelson, 2002).
Perception & Psychophysics 10/2008; 70(7):1289-97. · 1.37 Impact Factor
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ABSTRACT: Kohn and Movshon [Kohn, A., & Movshon, J. (2003). Neuronal adaptation to visual motion in area MT of the macaque. Neuron, 39, 681-691; Kohn, A., & Movshon, J. A. (2004). Adaptation changes the direction tuning of macaque MT neurons. Nature Neuroscience, 7(7), 764-772] measured the contrast response functions of single neurons in MT (V5) before and after adaptation to high contrast gratings. They found that when gratings were smaller than the MT receptive field, so that adapting and test regions could be either co-localised or non-overlapping, adaptation was spatially specific. This led to the hypothesis that grating adaptation occurs in V1, where receptive fields are small and retinotopically organized, and that MT merely inherits this adaptation. We predicted that spatial specificity would be less for dot stimuli that probably adapt MT cells directly. Also, given recent contradictory claims that hMT primarily exhibits both spatiotopy [d'Avossa, G., Tosetti, M., Crespi, S., Biagi, L., Burr, D., & Morrone, M. (2006). Spatiotopic selectivity of BOLD responses to visual motion in human area MT. Nature Neuroscience, 10, 249-255] and retinotopy [Gardner, J. L., Merriam, E. P., Movshon, J. A., & Heeger, D. J. (2008). Maps of visual space in human occipital cortex are retinotopic, not spatiotopic. The Journal of Neuroscience, 28, 3988-3999], we were interested in producing relevant psychophysical evidence using the direction aftereffect. In three experiments, we measured direction aftereffects (DAEs) induced and tested either with drifting gratings or drifting dots when stimulus location was changed both retinotopically and spatiotopically between adaptation and test; when retinotopic location only was changed; and when spatiotopic location only was changed. We predicted and found that spatial specificity was greater for gratings than for dots. We also found very small spatiotopic effects that call into question some recent claims that area MT exhibits a high degree of spatiotopicity.
Vision Research 07/2008; 48(19):1949-54. · 2.41 Impact Factor
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ABSTRACT: Reference repulsion is a mechanism posited to explain systematic biases of direction judgment of single drifting dot displays (Rauber and Treue, 1998 Perception 27 393-402). Rauber and Treue obtained systematic but, surprisingly, very different effects depending upon whether standard and comparison stimuli were presented simultaneously or successively. Successive effects were described as exhibiting repulsion from both vertical and horizontal cardinal axes, whereas simultaneous effects showed repulsion from horizontal only. We contend that the proposed mechanism makes no testable predictions because the so-called reference can only be specified a posteriori, a fact acknowledged by Rauber and Treue. We attempted to replicate Rauber and Treue's experiments, but we obtained no systematic biases of direction judgment. Comparisons across several studies suggest that errors in direction judgments of single drifting dot patterns vary widely in magnitude and direction, as might be expected with what are essentially baseline or pretest measures. In our view, reference repulsion describes neither a real perceptual mechanism nor a predictable pattern of direction misjudgments.
Perception 02/2008; 37(9):1380-5. · 1.31 Impact Factor
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ABSTRACT: Direction repulsion is the illusory expansion of the angle between two directions of motion, and may occur when the two directions are presented simultaneously (an illusion) or successively (an aftereffect). Here we demonstrate that the motion direction illusion (DI) and aftereffect (DAE) have different mechanisms. Two experiments show that when the two interacting stimuli are presented to different eyes, the DI is greatly reduced but the DAE is obtained at near to full strength. These results suggest that different populations of cells within the visual pathway produce the DI and DAE.
Vision Research 07/2007; 47(14):1963-7. · 2.41 Impact Factor
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ABSTRACT: Prinzmetal and Beck (2001) Journal of Experimental Psychology: Human Perception and Performance 27 206 - 217) argued that a subset of visual illusions is caused by the same mechanisms that are responsible for the perception of vertical and horizontal a theory they referred to as the tilt-constancy theory of visual illusions. They argued that these illusions should increase if the observer's head or head and body are tilted because extra reliance would then be placed on the illusion-inducing local visual context. Exactly that result had previously been reported in the case of the tilted-room and the rod-and-frame illusions. Prinzmetal and Beck reported similar increases in the tilt illusion (TI), as well as the Zöllner, Poggendorff, and Ponzo illusions. In two experiments, we re-examined the effect of head tilt on the TI. In experiment 1, we used more conventional TI stimuli, more standard experimental methods, and a more complete experimental design than Prinzmetal and Beck, and additionally extended the investigation to attraction as well as repulsion effects. Experiment 2 more closely replicated the Prinzmetal and Beck stimuli. Although we found that head tilt did increase TIs in both experiments, the increases were of the order of 1 degrees -2 degrees, more modest than the 7 degrees reported by Prinzmetal and Beck. Significantly, the TI increase was larger when inducing tilts and head tilts were in the same direction than when they were in opposite directions, suggesting that the tilt-constancy theory may be oversimplified. In addition, because previous evidence renders unlikely the claim that the Poggendorff illusion can be explained simply in terms of misperceived orientation of the transversals, the question arises whether there might be some other explanation for the increase in the Zöllner, Poggendorff, and Ponzo illusions with body tilt that Prinzmetal and Beck reported.
Perception 02/2006; 35(2):201-13. · 1.31 Impact Factor
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ABSTRACT: We investigated whether the same principles that influence grouping in static displays also influence grouping in apparent motion. Using the Ternus display, we found that the proportion of group motion reports was influenced by changes in contrast configuration. Subjects made judgments of completion of these same configurations in a static display. Generally, contrast configurations that induced a high proportion of group motion responses were judged as more 'complete' in static displays. Using a stereo display, we then tested whether stereo information and T-junction information were critical for this increase in group motion. Perceived grouping was consistently higher for same contrast polarity configurations than for opposite contrast polarity configurations, regardless of the presence of stereo information or explicit T-junctions. Thus, while grouping in static and moving displays showed a similar dependence on contrast configuration, motion grouping showed little dependence on stereo or T-junction information.
Perception 02/2005; 34(6):669-85. · 1.31 Impact Factor
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ABSTRACT: Five experiments were conducted in order to determine which of two hypotheses, initially proposed by Rock (1990), accounts for interactions between oriented elements in a visual scene. We also explored the suggestion that two hypothetical processes--namely, frame of reference and hierarchical organization--describe phenomena arising from distinct mechanisms (Spinelli, Antonucci, Daini, Martelli, & Zoccolotti, 1999). Double inducing stimulus versions of one-dimensional and two-dimensional tilt illusions, the rod-and-frame illusion, and combinations of these were used. Our data suggest that both hypotheses can predict orientation interactions in conditions in which only one mechanism--namely, the global visual mechanism of symmetry axes extraction (Wenderoth & Beh, 1977)--is activated. Which hypothesis is appropriate to predict the perceived orientation depends on some physical features of the objects.
Perception & Psychophysics 07/2003; 65(5):770-8. · 1.37 Impact Factor
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ABSTRACT: The misperceived direction of type-II plaids has posed a problem for the intersection of constraints (IOC) model of two-dimensional motion perception. Alais et al. (1994)(Vision Research, 34, 1823–1834) examined the perceived direction of type-II plaids and concluded that in addition to the direction signalled by the IOC process, a monocular mechanism signalling the motion of plaid features (blobs) is also involved in plaid perception. It was shown that the prominence of this monocular signal in plaid direction judgements depended on several variables, and the notion of blob “optimality” was introduced. This explained the more veridical direction of “optimal” blob plaids in terms of their more effectively activating the proposed feature-sensitive motion mechanism. One distinction between “optimal” and “non-optimal” blob plaids is their different component spatial frequencies, which necessarily entails a difference in the number and size of the blobs and thus raises potential confounds, since both the nature of the blobs and the components differ, which might affect the postulated blob mechanism and/or the IOC process. In the present paper, by offsetting changes in spatial frequency with changes in aperture size so that blob number is held constant, we examine whether differences in sheer blob number or size can alter perceived type-II plaid direction. The results reveal effects of both blob number and blob size, and their implications for the underlying mechanism are considered. Alternative accounts of the results in terms of the IOC model or revisions of it cannot explain the data. Comparison of monocular and binocular conditions adds further systematic evidence in support of the monocularity of the feature-sensitive motion mechanism. Copyright © 1996 Published by Elsevier Science Ltd
Vision Research 02/1997; · 2.41 Impact Factor
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ABSTRACT: This report adds to existing evidence that a monocular, feature-sensitive motion mechanism is involved in two-dimensional (2-D) motion processing, and also accounts for an earlier, unexplained result [Alaiset al. (1994)Vision Research, 34 1823–1834]. The central finding is that the perceived direction of a monocularly viewed type II plaid changes over a period of continuous exposure such that post-adaptation direction judgements exhibit more of the component-direction bias known to occur with these stimuli than pre-adaptation judgements. These adaptation effects are confined to the adapted eye: when the adapting stimulus is presented to one eye, pre- and post-adaptation direction judgements made with the other, non-adapted eye are identical. These results strongly suggest the involvement of a monocular motion mechanism in two-dimensional motion processing, in addition to the more commonly presumed binocular mechanisms.
Vision Research 06/1996; · 2.41 Impact Factor
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ABSTRACT: A number of recent studies have suggested that the “intersection of constraints” model of two dimensional motion perception, put forward by Adelson and Movshon [(1982) Nature, 300, 523–525], is incomplete. Evidence has been mounting that there is a second two-dimensional motion sensitive mechanism which is monocular and which appears to respond directly to the movement of the intersections (or “blobs”) in a two-dimensional image. The current study extends these findings by demonstrating that the perceived coherence of a drifting plaid is largely under the control of a monocular mechanism. Prior exposure to a similarly drifting grating or plaid substantially raises the coherence threshold of a test plaid only if the same eye is adapted and tested. The threshold elevation is much more modest if the test plaid is presented to the unadapted eye, suggesting that coherence judgements are primarily based on the activity level of a monocular process—possibly the “blob tracking mechanism”. The results of Expt 2 suggest the possibility that this monocular mechanism is inhibited by binocular exposure.
Vision Research 01/1995; · 2.41 Impact Factor
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ABSTRACT: When motion aftereffects (MAEs) are measured by adapting to a drifting plaid (simultaneous adaptation) or by adapting to the plaid's component gratings in alternation (alternating adaptation), it has been shown that the velocity and duration of the MAE are smaller in the latter case [Wenderoth, P., Bray, R. & Johnstone, S. (1988) Perception, 17, 81–91; Burke, D. & Wenderoth, P. (1993) Vision Research, 33, 351–359]. However, Burke and Wenderoth additionally reported that the directions of MAEs induced by simultaneous and alternating adaptation were identical, an apparent inconsistency if the differences in duration and velocity were due to the presence of “blobs” at the component grating intersects in the simultaneous case. Presumably, the direction of the “blobs” should also affect perceived plaid direction during adaptation and, hence, the MAE direction. In five experiments, we have measured both perceived adapting plaid and MAE direction, tested with both alternating and simultaneous adaptation, measured interocular transfer of plaid-induced MAEs and obtained MAE and plaid direction judgments under monocular and binocular viewing conditions. All of the data indicate that there is a blob tracking mechanism which is preferentially stimulated by plaids whose component gratings have high spatial frequency, low temporal frequency and high contrast. Differences between simultaneous and alternating adaptation emerge only when more optimal blobs are used, thus accounting for Burke and Wenderoth's failure to find a difference. The data also support Burke and Wenderoth's claim that the blob tracking mechanism is monocular: alternating and simultaneous adaptation produce identical MAEs under interocular transfer conditions, even using plaids with more optimal blobs. We also report the unexpected finding that plaids with more- and less-optimal blobs appear to drift in directions 20° apart yet their aftereffects differ in direction by only 3–5°. That is, more optimal blob plaids—compared with less optimal blob plaids—change both perceived plaid direction during adaptation and subsequent perceived MAE direction but the latter change is much more modest. Possible explanations of this dissociation are considered.
Vision Research 07/1994; · 2.41 Impact Factor
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ABSTRACT: Motion aftereffects (MAEs) can be induced by adaptations to a pair of differently oriented drifting gratings whether the gratings are presented simultaneously, as a coherent plaid, or in alternation. The fact that the former MAEs were generally larger than the latter led to the suggestion that simultaneous adaptatian involved higher-level extrastriate processes not involved in the alternating effects. In the past few years evidence has accumulated that the difference is in fact due to a low-level monocular precast which may be termed the 'blob-teaching mechanism'. A review is presented of the evidence an MAEs induced by simultaneous and alternating adaptation, the evidence for the monocularity of the blob-teaching mechanism, the data which implicate the blob monocularity in the determinatian of MAE magnitude, perceived plaid drift direction, and in perceived plaid coherence.
Perception 02/1994; · 1.31 Impact Factor
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ABSTRACT: Ferrera and Wilson [(1990) Vision Research, 30, 273–287] reported veridical perception of the direction of motion of Type I plaids, whose component gratings span the resultant direction, but marked misperception of the direction of motion of Type II plaids, whose component gratings both lie on one side of the resultant direction. Because they failed to find any effect of component direction (angular) separation on this misperception, Ferrera and Wilson concluded that the misperception was not due to perceptual repulsion of component directions. We report that component direction repulsion does occur, that plaid direction misperception is tuned to component separation, with larger repulsions for smaller angles. It is concluded that there is no fundamental difference in direction coding for Type I and Type II plaids, and that Ferrera and Wilson failed to find a direction separation effect because the range of separations they used was insufficiently broad to detect the slope of the angular function.
Vision Research 03/1993; · 2.41 Impact Factor
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ABSTRACT: Wenderoth, Bray and Johnstone [(1988) Perception, 17, 81–91) measured motion aftereffects induced on stationary vertical sine-wave gratings by horizontally drifting two-dimensional patterns (plaids). The adapting plaid component gratings were simultaneously or alternately presented and were oriented left and right of vertical by 15, 45 or 75°. It was found that aftereffects decreased linearly in the alternating conditions as the plaid component orientations changed but this was not the case in the simultaneous adaptation conditions, a finding taken to be consistent with the hypothesis that one-dimensional aftereffects have a low level site (possibly V1) whereas two-dimensional effects have a higher level site (possibly MT). In three experiments, we have examined in more detail the determinants of aftereffects induced by simultaneous and alternating plaid components. The data suggest that the mechanisms involved are more complex than those put forward by Wenderoth et al. and that plaid perception utilizes both higher and lower level processes which can be referred to, respectively, as an intersection of constraints algorithm and a moving “blob” detector.
Vision Research 03/1993; · 2.41 Impact Factor
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ABSTRACT: Lucca, Dellantonio, and Riggio (1986) reported large distortions in a tactual analogue of the visual Poggendorff illusion.
They also reported large effects in the direction opposite to the visual illusion, which they termed “inversions”. However,
their evidence for such effects is questionable; they used what we consider to be inappropriate measurement and analysis procedures.
In attempting to replicate their experiment, and in conducting four additional experiments, we found no evidence at all for
their alleged tactual analogue of the visual Poggendorff effect. Instead, we demonstrated that “inversions” are likely due
to the use of a raised stimulus display that causes artifactual mistracking, which is totally unrelated to normal mechanisms
of alignment judgment. We also discuss the possible role of intersensory factors in the generation of tactual illusions.
Attention Perception & Psychophysics 04/1990; 48(3):234-242. · 2.04 Impact Factor
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School of Health and Human Sciences Papers.
