Autokinetic movement in geometric illusions: a note.

Four static geometrical illusions were presented in an autokinetic movement situation. 50 Ss saw each form four times. Of the total responses, 36% were no-movement responses while 37% of the time the total figure was seen as moving. The meaning 27% of the responses involved apparent movement in only a part of the figure. In general, the elements seen as moving are the parts misperceived in the static geometrical illusion.     

Attentional biases in geometric form perception

This paper reports the operation of robust attentional bias to the top and right during perception of small, single geometric forms. Same/different judgements of successively presented standard and comparison forms are faster when local differences are located at top and right rather than in other regions of the forms. The bias persists when form size is reduced to approximately one degree of visual angle, and it is unaffected by saccadic eye movements and by instructions to attend to other reliably differentiating regions of the forms. Results lend support in various degrees to two of the possible explanations of the bias: (1) a static, skewed distribution of attentional resources around eye fixation; and (2) biased, covert scanning that commences invariably at the top and right of stim ulus forms. Origins of the bias in terms of possible left-hemispheric capacity for constructing representations of visual stimuli from parts, as well as in terms of reading experience and prevailing optic flow during locomotion through space are considered. Recent investigations of conditions under which the bias can be maintained or reduced are mentioned.     

The perception of emotion from body movement in point-light displays of interpersonal dialogue

We examined whether it is possible to identify the emotional content of behaviour from point-light displays where pairs of actors are engaged in interpersonal communication. These actors displayed a series of emotions, which included sadness, anger, joy, disgust, fear, and romantic love. In experiment 1, subjects viewed brief clips of these point-light displays presented the right way up and upside down. In experiment 2, the importance of the interaction between the two figures in the recognition of emotion was examined. Subjects were shown upright versions of (i) the original pairs (dyads), (ii) a single actor (monad), and (iii) a dyad comprising a single actor and his/her mirror image (reflected dyad). In each experiment, the subjects rated the emotional content of the displays by moving a slider along a horizontal scale. All of the emotions received a rating for every clip. In experiment 1, when the displays were upright, the correct emotions were identified in each case except disgust; but, when the displays were inverted, performance was significantly diminished for some emotions. In experiment 2, the recognition of love and joy was impaired by the absence of the acting partner, and the recognition of sadness, joy, and fear was impaired in the non-veridical (mirror image) displays. These findings both support and extend previous research by showing that biological motion is sufficient for the perception of emotion, although inversion affects performance. Moreover, emotion perception from biological motion can be affected by the veridical or non-veridical social context within the displays.     

Young infants' perception of unity and form in occlusion displays

Young infants have been reported to perceive the unity of a center-occluded object when the visible ends of the object are aligned and undergo common motion but not when the edges of the object are misaligned (Johnson & Aslin, 1996). Using a recognition-based paradigm, the authors investigated the possibility that past research failed to provide sufficiently sensitive assessments of infants' perception of the unity of misaligned edges in partial occlusion displays. Positive evidence was obtained in 4-month-olds for veridical perception of the motion and location of a hidden region but not its orientation, whereas 7-month-olds, in contrast to the younger infants, appeared to respond to the orientation of the hidden region. Overall, the results suggest that habituation designs tapping recognition processes may be particularly efficacious in revealing infants' perceptual organization. In addition, the findings provide corroborative evidence for the importance of both motion and orientation in young infants' object segregation and for the difficulty in achieving percepts of the global form of a partly occluded object.     

Illusory illusions: the significance of fixation on the perception of geometrical illusions

Some well-known geometrical illusions disappear when the eyes are fixating and saccades are suppressed for a period of time. This disappearance is not accompanied by fading due to stabilisation of the retinal image. Any saccade made on purpose restores the illusion immediately. The fixation time after which some illusions disappeared was measured for four illusions and four subjects each. Effects of practice have been observed after measurements were repeated on successive days. Present theories of vision cannot readily explain the effect.     

The assimilation theory of geometric illusions: An additional postulate

The assimilation theory of geometric illusions is extended to include an additional postulate which states that “assimilative effects increase with an increase in the range of contextual magnitudes”. The effects of several stimulus variables on the Müller-Lyer and Poggendorff illusions are explained on the basis of this postulate.     

Further developments in the assimilation theory of geometric illusions: The adjacency,principle

It is argued that the parallel lines illusion is the basic model for many visual distortions that are produced by geometric patterns. An experiment assessed the effect of moving the contextual contour away from the standard contour in two directions—away from the center of the attentive field and toward the center of the attentive field. The degree of illusion declined as the contextual magnitude moved away from the standard magnitude, but the rate of decline was more rapid when the contextual stimulus was moved away from the center of the attentive field. The results necessitated the addition of a new postulate for the assimilation theory of geometric illusions. This postulate states that the effectiveness of a contextual magnitude decreases as the distance between the contextual magnitude and the standard magnitude increases. The postulate was translated into a mathematical form in a manner analogous to the way in which the “attentive field” postulate was quantified. The new formula was successful in predicting both the pattern of means and the pattern of variances found in this study. The formula was cross-validated with data from the Ponzo and reversed Mueller-Lyer illusions.     

Visual illusions and direct perception: Elaborating on Gibson's insights

Gibson argued that illusory pictorial displays contain “inadequate” information (1966, p. 288) but also that a “very special kind of selective attention” (p. 313) can dispel the illusion–suggesting that adequate perceptual information could in fact be potentially available to observers. The present paper describes Gibson's treatment of geometrical illusions and reviews pertinent empirical evidence. Interestingly, Gibson's insights have been corroborated by recent findings of inter- and intra-observer variability in susceptibility to visual illusions as a function of culture, learning and task. It is argued that these findings require a modification of the general Gibsonian principle of perception as the detection of specifying information. Withagen and Chemero's (2009) evolutionary motivated reconceptualization of perception predicts observers' use of both specifying and non-specifying information and inter- and intra-observer variability therein. Based on this reconceptualization we develop an ecological approach to visual illusions that explains differential illusion effects in terms of the optical variable(s) detected.     

Emotion perception from dynamic and static body expressions in point-light and full-light displays

Research on emotion recognition has been dominated by studies of photographs of facial expressions. A full understanding of emotion perception and its neural substrate will require investigations that employ dynamic displays and means of expression other than the face. Our aims were: (i) to develop a set of dynamic and static whole-body expressions of basic emotions for systematic investigations of clinical populations, and for use in functional-imaging studies; (ii) to assess forced-choice emotion-classification performance with these stimuli relative to the results of previous studies; and (iii) to test the hypotheses that more exaggerated whole-body movements would produce (a) more accurate emotion classification and (b) higher ratings of emotional intensity. Ten actors portrayed 5 emotions (anger, disgust, fear, happiness, and sadness) at 3 levels of exaggeration, with their faces covered. Two identical sets of 150 emotion portrayals (full-light and point-light) were created from the same digital footage, along with corresponding static images of the 'peak' of each emotion portrayal. Recognition tasks confirmed previous findings that basic emotions are readily identifiable from body movements, even when static form information is minimised by use of point-light displays, and that full-light and even point-light displays can convey identifiable emotions, though rather less efficiently than dynamic displays. Recognition success differed for individual emotions, corroborating earlier results about the importance of distinguishing differences in movement characteristics for different emotional expressions. The patterns of misclassifications were in keeping with earlier findings on emotional clustering. Exaggeration of body movement (a) enhanced recognition accuracy, especially for the dynamic point-light displays, but notably not for sadness, and (b) produced higher emotional-intensity ratings, regardless of lighting condition, for movies but to a lesser extent for stills, indicating that intensity judgments of body gestures rely more on movement (or form-from-movement) than static form information.     

The visual perception of velocity

Summary In this section it is concluded that velocity is perceived directly and is dynamically conditioned by the structure and general properties of the visual field in which the movement occurs. The visual perception of velocity follows dynamic laws that are not immediately deducible from the velocity of the stimulus as physically defined. No physiological theory is offered but it is pointed out that the theory of physiological Gestalten is essentially correct in its basic assumptions concerning the perception of movement.The investigation has bearing on the problems of movement thresholds, movement after-images and the perception of time.This paper is abridged from a thesis presented to the faculty of the graduate school of Yale University in partial fulfilment of the requirements for the degree of Doctor of Philosophy. The study was started in the Psychological Institute of the University of Berlin in 1926–1927 and completed at Yale University in 1928–1929. The work at Berlin, which has been already reported [cf. J. F. Brown, Über gesehene Geschwindigkeit. Psychol. Forschg 10, 84–101 (1927)] was largely exploratory in nature; that at Yale was undertaken to fill the gaps in the experimental series and to control more completely the causal factors. For clarity of exposition the previously reported data are included here so far as necessary. The writer is indebted to Professor W. Köhler of the University of Berlin for suggesting the problem, and to Professors R. P. Angier, R. Dodge, and L. T. Spencer of Yale University for many valuable suggestions. He wishes also to express his thanks to the subjects who served in the experiments.     

Wayfinding: The effects of large displays and 3-D perception

Large displays and stereopsis have been shown to improve performance in several virtual navigation tasks. In the present research, we sought to determine whether wayfinding could benefit from these factors. Participants were tested in a virtual town. There were three viewing conditions: a desktop, a large screen, and a large screen on which the virtual environment was viewed in three dimensions (3-D) using polarized glasses. Participants explored the town and had to remember the location of several landmarks. Their memory of the layout of the town was tested by asking them to navigate from one landmark to another, taking the shortest route possible. All groups performed equally well in terms of the distance traveled to target locations. From this result, we concluded that large displays and 3-D perception do not significantly contribute to wayfinding. Thus, experimental paradigms and training programs that utilize wayfinding are as valuable when administered on standard desktops as on more sophisticated and costly equipment and do not induce simulator sickness as large displays tend to do.     

The perception of identity in simultaneously presented complex visual displays

Two experiments were conducted in order to examine the information processing in a visual matching task, using digit sequences of varying complexity as the stimuli. Traditionally, reaction times for “same” judgments do not fit into a single-process self-terminating feature testing model, while those for “different” judgments do. Bamber (1969) proposed a two-stage model to account for the data, and the results of these experiments support this type of model. Strong evidence implying that Bamber’s “identity reporter” has a limited capacity in terms of stimulus complexity was also found. This complexity seems to be deemed by stimulus discriminability and the number of “chunks” of information rather than by “bits” of information being transmitted (Miller, 1956).