An experimental and theoretical appraisal of the perspective and size-constancy theories of illusions

The perspective and size-constancy theories of illusions are described. They both imply that illusory distortions arise as a consequence of mistaken perceptual impressions of depth. Predictions from these theories are tested in six experiments and several ancillary studies. They show that although differences in apparent distance may be sufficient for the appearance of illusions their presence is not a necessary condition. Detailed theoretical implications of these results are considered in discussion.     

Prediction and diagnosis: An experimental comparison

Diagnostic tasks differ from predictive tasks in two respects (1) the direction of the inference in diagnosis (from effect to cause) is inverse to that in prediction (from cause to effect), and (2) the event to be inferred is more distal in diagnostic tasks than in predictive tasks. These task features led to the hypothesis that a diagnostic task would be harder to learn than a predictive task. This hypothesis was tested in an experimental situation in which the causal mechanism was random sampling with replacement. Five groups of subjects with 10 subjects in each (two predictive and three diagnostic groups) were run in individual sessions with 100 trials of feedback training. The two predictive groups learned more rapidly and to a higher level compared to the diagnostic groups. Conclusion: the present data support the hypothesis that predictive tasks are easier to learn than comparable diagnostic tasks.     

An empirical taxonomy of visual illusions

A classification system for visual-geometric illusions, based upon the interrelationships between behavioral responses to various distortions was created. Forty-five illusion configurations were presented to 221 observers. Factor analysis revealed that there are five classes of illusions. A secondorder analysis revealed that visual distortions are ultimately reducible to two global types of distortions: illlusions of extent and illusions of shape or direction.     

Mending metacognitive illusions: a comparison of mnemonic-based and theory-based procedures

Previous research indicated that learners experience an illusion of competence during learning (termed foresight bias) because judgments of learning (JOLs) are made in the presence of information that will be absent at test. The authors examined the following 2 procedures for alleviating foresight bias: enhancing learners' sensitivity to mnemonic cues pertaining to ease of retrieval and inducing learners to resort to theory-based judgments as a basis for JOLs. Both procedures proved effective in mending metacognitive illusions-as reflected in JOLs and self-regulation of study time-but only theory-based debiasing yielded transfer to new items. The results support the notion that improved metacognition is 1 key to optimizing transfer but also that educating subjective experience does not guarantee generalization to new situations.     

Susceptibility to semantic illusions: An individual-differences perspective

When askedHow many animals of each kind did Moses take on the ark?, people frequently respond “two” even though they know it was Noah, not Moses, who took animals on the ark. We replicate previous research by showing that susceptibility to semantic illusions is influenced by the semantic relatedness of both the impostor word and the surrounding context. However, we also show that the two text manipulations make independent contributions to semantic illusions, and we propose two individual-differences mechanisms that might underlie these two effects. We propose that the ability to resist the lure of a semantically related impostor word is related to the individual’s skill at accessing and reasoning about knowledge from long-term memory. And we propose that the ability to resist the lure of the surrounding sentential context is related to the individual’s capacity to simultaneously process and store information in working memory.     

An experimental comparison of three- versus four-surface phenomenal transparency

The three-surface transparency occurs when an object seen through a transparency does not jut out under the transparent surface. The four-surface transparency occurs when the object juts out. Observers rated the density of the transparent surface in both kinds of transparency. The results seem to show that the topological diversity between the two kinds of transparency has no functional significance. The stimulus conditions ruling the generation of judgments were detected and expressed in terms of an algebraic model.     

An experimental comparison of viewpoint-specific and viewpoint-independent models of object representation

Four experiments that investigate the cognitive representation of objects in human observers are reported. Two broad classes of theory were examined: viewpoint-specific and viewpoint-independent models. The former postulate that the data structures underpinning object recognition correspond to discrete views and require additional processing to access them from unfamiliar viewpoints. The latter postulate data structures that are independent of any particular viewpoint and can be directly accessed from a wide range of viewpoints. Two experimental tasks were used: a sequential matching paradigm and a cognitive learning paradigm. Findings favour viewpoint-specific models over viewpoint-independent models.     

Idealism and illusions

According to the idealist, facts about phenomenal experience determine facts about the physical world. Any such view must account for illusions: cases where there is a discrepancy between the physical world and our experiences of it. In this article, I critique some recent idealist treatments of illusions before presenting my own preferred account. I then argue that, initial impressions notwithstanding, it is actually the realist who has difficulties properly accounting for illusions.     

An intra-cultural investigation of susceptibility to 'perspective' and 'non-perspective' spatial illusions

Conventional Müller-Lyer and modified Müller-Lyer (without 'perspective' cues) illusions were presented to two samples of children aged between eight and 19, matched in education, but living in 'carpentered' and 'uncarpentered' environments in Zambia. Traditional differences in susceptibility have been obtained with both the variations of the Müller-Lyer illusion. In view of the lack of perspective cues in one of these, it is concluded that the perspective theory as presented within the 'carpentered world hypothesis' is inadequate. Since these differences are intra-cultural, they also do not support the hypothesis which suggests that cross-cultural variations in illusion susceptibility are due to genetic factors--such as macular (or retinal) pigmentation.     

Nasal,retronasal, and gustatory perception: An experimental comparison

Four odor substances (lemon aroma, rum aroma, ethyl butyrate, and amyl acetate) in different concentrations were presented nasally and orally (retronasally) in a four-alternative forced-choice procedure (detection tasks). In a further experimental condition, sucrose was added to the stimuli. Finally, the taste properties of the (nonsugared) odor stimuli were judged on seven semantic scales. In the detection of odor-containing stimuli, there were no significant differences between nasal and retronasal stimulation. In the taste conditions, however, there was a significant decline of “hits” when the stimuli contained sucrose in addition to the odor substances. Furthermore, in semantic scaling of the taste stimuli, a new variant of the taste-smell illusion was observed, namely, a tendency to attribute “suited” basic taste categories (e.g., “sweet”) to pure (nongustatory) odor stimuli.     

An experimental comparison of stimulus and response translated power functions for brightness

A threshold parameter has been introduced into the power law in two different ways, one involving, translation on the stimulus axis (the Ф-Law) and the second involving translation on the response axis (the Ψ-Law). In this study the two laws were compared using the data from 6 Ss making magnitude estimation judgments of brightness. Although the prevalent view appears to favor the Ф -Lau, the data of this study clearly dictate a choice of the Ψ-Law over the $-Law for brightness.     

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.