Perception
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Ever since the assassination of US President Kennedy, numerous theories have circulated purporting that Lee Harvey Oswald, the accused assassin, acted as part of a larger criminal conspiracy. It has been suggested, for example, that incriminating photographs of Oswald were manipulated, and hence evidence of a broader plot. Specifically, it has been argued that the lighting and shadows in these photos are physically impossible. Because the visual system is often unable to reliably judge 3-D geometry and lighting, a detailed 3-D analysis of the Oswald photos to determine if claims of tampering are warranted.
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The distinction between different spatial representations in the peripersonal space was examined in two experiments by requiring sighted blindfolded and blind participants to remember the locations of objects haptically explored. In experiment 1, object relocation took place from either the same position as learning-with the same (centred egocentric condition) or 90 degrees-rotated (rotated egocentric condition) object array-or from a position different from the learning position (allocentric condition). Results revealed that, in both sighted and blind people, distance errors were higher in the allocentric and rotated conditions than in the centred egocentric condition, and that blind participants made more distance errors than sighted subjects only in the allocentric condition. ⋯ The decentred egocentric condition was found to remain significantly different from the rotated condition, but not from the allocentric condition. Moreover, blind participants performed less well in the allocentric condition, but were specifically impaired. Overall, our results confirm that different types of spatial constraints and representations, including the decentred egocentric one, can be distinguished in the peripersonal space and that blind people are as efficient as sighted in the egocentric and rotated conditions, but they encounter difficulties in recalling locations also in the peripersonal space, especially when an allocentric condition is required.
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We cite two different perceptual-correspondence principles whose emphasis can help to disambiguate the otherwise ambiguous Ternus display in apparent movement (a display that can alternately be seen in one of two possible configurations). One of these principles is spatial correspondence, which emphasizes the maintenance of similar stimulus elements in given locations over time. The other principle is relation correspondence, which emphasizes the maintenance of the inter-organization of stimulus elements across frames. ⋯ As predicted, an emphasis upon spatial correspondence resulted in an increase in reports of element movement compared to a featureless control condition. Emphasis on relation correspondence resulted in an increase in reports of group movement. Extensions and limitations of the use of these principles to explain apparent movement are discussed.
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Randomized Controlled Trial
"Which feels heavier--a pound of lead or a pound of feathers?" A potential perceptual basis of a cognitive riddle.
"Which weighs more--a pound of lead or a pound of feathers?" The seemingly naive answer to the familiar riddle is the pound of lead. The correct answer, of course, is that they weigh the same amount. ⋯ When blindfolded participants hefted a pound of lead and a pound of feathers each contained in boxes of identical size, shape, and mass, they reported that the box containing the pound of lead felt heavier at a level above chance. Like the size-weight illusion, the naive answer to the riddle may reflect differences in how easily the objects can be controlled by muscular forces and not a perceptual or cognitive error.
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Randomized Controlled Trial
Remembering object position in the absence of vision: egocentric, allocentric, and egocentric decentred frames of reference.
In three experiments we examined whether memory for object locations in the peri-personal space in the absence of vision is affected by the correspondence between encoding and test either of the body position or of the reference point. In particular, the study focuses on the distinction between different spatial representations, by using a paradigm in which participants are asked to relocate objects explored haptically. Three frames of reference were systematically compared. ⋯ Here, the allocentric condition was found to be more difficult than the decentred egocentric condition. Taken together, the results suggest that also in the peripersonal space and in the absence of vision different frames of reference can be distinguished. In particular, the decentred egocentric condition involves a frame of reference which seems to be neither allocentric nor totally egocentric.