Sander Parallelogram Research Articles

Priming of the Sander Parallelogram illusion separates perception from action.

The two-visual stream hypothesis posits that the dorsal stream is less susceptible than the ventral stream to the effects of illusions and visual priming. While previous studies have separately examined these perceptual manipulations, the present study combined the effects of a visual illusion and priming to examine the possibility of dorsally guided actions being susceptible to the perceptual stimuli due to interactions between the two streams. Thirty-four participants were primed with a 'long' or 'short' version of the Sander Parallelogram illusion and were asked to either reach out and grasp or manually estimate the length of a rod placed on a version of the illusion that was on some trials the same as the prime (congruent) and on other trials was the inverse (incongruent). Due to the context-focused nature of ventral processing, we predicted that estimations would be more susceptible to the effects of the illusion and priming than grasps. Results showed that while participants' manual estimations were susceptible to both priming and the illusion, the grasps were only affected by the illusion, not by priming. The influence of the illusion on grip aperture was greater during manual estimations than it was during grasping. These findings support the notion that the functionally distinct dorsal and ventral streams interact under the current experimental paradigm. Outcomes of the study help better understand the nature of stimuli that promote interactions between the dorsal and ventral streams.

The influence of the Sander parallelogram illusion and early, middle and late vision on goal-directed reaching and grasping

Vision is one of the most robust sensory inputs used for the execution of goal-directed actions. Despite a history of extensive visuomotor research, how individuals process visual context for the execution of movements continues to be debated. This experiment examines how early, middle and late visuomotor control is impacted by illusory characteristics in a reaching and grasping task. Participants either manually estimated or reached out and picked up a three-dimensional target bar resting on a two-dimensional picture of the Sander parallelogram illusion. Participants performed their grasps within a predefined time movement window based on their own average grasp time, allowing for the manipulation of visual feedback. On some trials, vision was only available before the response cue (an auditory tone), while on others vision was occluded until the response cue, becoming available for either the full, early, middle or late portions of the movement. While results showed that the effect of the illusion was stronger on manual estimations than on grasping, maximum grip apertures in the occluded vision and early vision grasping conditions were also consistent to a lesser extent with the illusion. The late vision condition showed longer movement time, wrist deceleration period, time to maximum grip aperture and lower maximum velocity. These findings indicate that visual context affects visuomotor control distinctly depending on when vision is available, and supports the notion that human vision is comprised of two functionally and anatomically distinct systems.

The Sander parallelogram illusion dissociates action and perception despite control for the litany of past confounds

The two visual systems hypothesis proposes that human vision is supported by an occipito-temporal network for the conscious visual perception of the world and a fronto-parietal network for visually-guided, object-directed actions. Two specific claims about the fronto-parietal network's role in sensorimotor control have generated much data and controversy: (1) the network relies primarily on the absolute metrics of target objects, which it rapidly transforms into effector-specific frames of reference to guide the fingers, hands, and limbs, and (2) the network is largely unaffected by scene-based information extracted by the occipito-temporal network for those same targets. These two claims lead to the counter-intuitive prediction that in-flight anticipatory configuration of the fingers during object-directed grasping will resist the influence of pictorial illusions. The research confirming this prediction has been criticized for confounding the difference between grasping and explicit estimates of object size with differences in attention, sensory feedback, obstacle avoidance, metric sensitivity, and priming. Here, we address and eliminate each of these confounds. We asked participants to reach out and pick up 3D target bars resting on a picture of the Sander Parallelogram illusion and to make explicit estimates of the length of those bars. Participants performed their grasps without visual feedback, and were permitted to grasp the targets after making their size-estimates to afford them an opportunity to reduce illusory error with haptic feedback. The results show unequivocally that the effect of the illusion is stronger on perceptual judgments than on grasping. Our findings from the normally-sighted population provide strong support for the proposal that human vision is comprised of functionally and anatomically dissociable systems.

Seeing the World Dimly: The Impact of Early Visual Deficits on Visual Experience in Schizophrenia

Deficits in early visual processing are well documented in schizophrenia, using methods such as contrast sensitivity. Higher, integrative stages of functioning, such as susceptibility to visual illusions, have been evaluated less extensively. For example, patients show increased susceptibility to (ie, are more easily affected by) the Muller-Lyer illusion but decreased susceptibility (ie, are less easily affected by) to stereopsis based upon binocular disparity. The basis for pattern of illusion response and interaction between sensory and integrative stages of processing, however, is unclear. We tested a group of 38 patients and 28 control subjects in contrast sensitivity, the Muller-Lyer and Poggendorff illusions, as well as a subgroup in stereopsis and the Ponzo illusion, Sander parallelogram, and Hermann grid illusions. We predicted that patients would be more susceptible to tests that become more apparent with increased contrast (Muller-Lyer illusion), less susceptible to tests that become less apparent with increased contrast (stereopsis, Ponzo illusion, Hermann grid), and equally susceptible to contrast-insensitive tests (Poggendorff illusion). Additionally, the Hermann grid was tested at varying levels of contrast. Patients demonstrated significant deficits in contrast sensitivity, especially to brief, low spatial frequency stimuli, and the predicted differential response to the tested illusions. Additionally, poor performance on stereopsis and the Hermann grid significantly correlated with decreased contrast sensitivity (all P's <.01). Muller-Lyer illusion and stereopsis performance were also inversely related (P < .01). This study replicates and expands upon previous findings with visual illusions. Our results offer a unifying explanation for disparate studies and suggest that deficits in early sensory gain affect subsequent integrative processes.

Geometrical illusions can affect time-to-contact estimation and mimed prehension.

Results indicate that under some conditions the Sander parallelogram illusion can affect time-to-contact (TTC) estimation in a prediction-motion (PM) task and in an interceptive action (IA). The illusion also affected mimed manual prehension. The implication is that the timing of responses in the PM and IA tasks may involve an estimate of TTC that is based on the perceived dimensions of the environment. Further research is warranted in the development of models of perceived collision and of visually guided actions.

Illusions and Knowing What Is Real

Geometrical illusions are displays that give false impressions that observers take to be accurate. They have traditionally been cited as evidence against the naive realist claim that people see the world as it "really" is. Such illusions, however, often depend on their being viewed from a single vantage point (Kennedy & Portal, 1990). In Gibsonian terms, they depend on the availability of impoverished information. In this study, spatial transformations were applied to line-length (Sander parallelogram) and area (Jastrow curves) illusions to provide information to observers about veridical size. In particular, the reversal of certain parts of the displays resulted in informative invariants that specified the veridical nature of the parts. Most observers were able to use the information.

The Case for Misapplied Constancy Scaling: Depth Associations Elicited by Illusion Configurations

It has been suggested that many visual-geometric illusions arise from inappropriate evocation of size-constancy by depth cues implicit in illusion configurations. Observers gave free association responses while viewing illusion figures. Analysis of these responses provides weak but consistent evidence for the elicitation of depth in the Sander parallelogram, Mueller-Lyer, Zoellner, and Ehrenfels variant of the Ponzo illusion. No evidence for depth is found in the normal form of the Ponzo, Poggendorff, and horizontal-vertical illusions, and the evidence is ambiguous in the Orbison configurations. These results indicate that depth processing may be evoked by some, but not all, classical illusion forms.

Developmental Influences on Geometric Illusion Susceptibility among Hong Kong Chinese Children

Hong Kong Chinese developmental results are presented to test cross-cultural developmental theories relating to changes in illusion susceptibility with age. The Muller-Lyer (M-L) and Sander-Parallelogram (S-P) illusion data confirm the expected decrease with age from 3-12 (Walter, 1942), and the later increase to age 21 due to exposure to a more sophisticated environment (Wapner and Werner, 1957). The data also supported Piaget and Morf's (1956) developmental hypotheses regarding contiguous and noncontiguous versions of the Horizontal-Vertical (H-V) illustions. The United States, Hong Kong, and Arunta cross-cultural comparisons also support the "carpentered world hypothesis," while H-V illusion susceptibility was also related to ecologically valid desert/urban differences in habits of perceptual inference. However, intersample differences in retinal pigmentation and the cross-sectional nature of the study may have influenced the results.

The assimilation theory applied to a modification of the Müller-Lyer illusion

The assimilation theory of illusions, which utilizes the principle that large magnitudes in a series are underestimated and small magnitudes are overestimated, was applied to a modification of the Müller-Lyer illusion. A close link was shown to exist between the Müller-Lyer illusion, a modification of the Müller-Lyer illusion, and the Sander parallelogram. In addition, a new illusory target was predicted.

Error increase and decrease in minimal form of Mueller-Lyer illusion.

Based upon prior research showing that the error associated with the Sander parallelogram is maximal when the diagonal lines are physically omitted rather than physically present, an attempt was made to determine if a similar finding might result from eliminating the shaft in the Mueller-Lyer illusion. An interaction was found between shaft vs no-shaft condition and fins-in vs fins-out. Eliminating the shaft significantly increased error in the fins-in condition and significantly decreased error in the fins-out condition. The results were judged consonant with the previous study involving the Sander parallelogram.