In De Anima III.3 Aristotle presents his official discussion of phantasia (“imagination” in most translations). At the very outset of the discussion Aristotle offers as an endoxon that “phantasia is that in virtue of which we say that a phantasma occurs to us” (428a1-2). Now a natural reading of this claim, taken up by many commentators, can pose a problem for Aristotle’s overall account of perception. Here I argue that, although it would be silly to deny that Aristotle considers (...) phantasia to be that in virtue of which a phantasma occurs to someone, it is not silly to deny that phantasmata are present in every case in which phantasia is operative. This suggestion bolsters the idea that, according to Aristotle’s account of veridical perception, we can understand the world as making itself perceptually manifest to the perceiver. (shrink)

Neurological disorders of body representation have for a long time suggested the importance of multisensory processing of bodily signals for self-consciousness. One such group of disorders – illusory own body perceptions affecting the entire body – has been proposed to be especially relevant in this respect, based on neurological data as well as philosophical considerations. This has recently been tested experimentally in healthy subjects showing that integration of multisensory bodily signals from the entire body with respect to the three (...) aspects: self-location, first-person perspective, and self-location, is crucial for bodily self-consciousness. Here we present clinical and neuroanatomical data of two neurological patients with paroxysmal disorders of full body representation in whom only one of these aspects, self-identification, was abnormal. We distinguish such disorders of global body representation from related but distinct disorders and discuss their relevance for the neurobiology of bodily self-consciousness. (shrink)

Despite the various perceptual-motor deficits documented in strabismus, there is a paucity of studies evaluating visual illusions in patients with strabismus. The aim of this study was to examine how the illusionary perception occurs in children/adolescents with strabismus with referral for surgery to correct ocular deviations. A controlled cross-sectional study was carried out in which 45 participants with strabismus and 62 healthy volunteers aged 10–15 years were evaluated. The behavioral response to three geometric illusions [Vertical-Horizontal illusion, Müller-Lyer illusion and (...) Ponzo illusion] and respective neutral stimuli regarding the estimation of image size and response time were measured using the Method of Adjustment. To analyze the influence of secondary factors: type of ocular deviation ; amount of eye deviation; presence of amblyopia and stereopsis, a one-way ANOVA was performed. Among the tested illusions, children with strabismus showed greater susceptibility and response time to Ponzo’s illusory images. Children with strabismus and preserved stereopsis, on the other hand, showed similar susceptibility and response time to control group patients to the Ponzo illusion. Patients with amblyopia showed overcorrection in the estimate of non-illusory Ponzo images. Children with horizontal ocular deviation associated with vertical deviation showed higher susceptibility to vertical adjustment images for the Müller-Lyer illusion. Individuals with strabismus tended to overcorrect the length of the straight-line segment adjusted for non-illusory images when testing non-illusory images in the Müller-Lyer test, as well as for the neutral images in the Vertical-Horizontal test. The findings indicated impairment in the perception of geometric illusions and neutral figures, especially for the Ponzo illusion test by children with strabismus. As the behavioral response to illusory images may indirectly reflect the visual and morphofunctional alterations present in these individuals, we suggest that the investigation of visual illusory perception can be used as a new research strategy in the field of investigating the visual function in strabismus. (shrink)

Leibniz has often been described as holding to a kind of phenomenalism. Yet Leibniz did not have a single account of perception, or of the embodied mind, or of the monad, but a set of conflicting and mutually inconsistent accounts that preclude the possibility that there is any such thing as “Leibniz's System.” This difficulty raises problems of interpretation, since it is sometimes maintained that the principle of charity precludes the assignment of frankly inconsistent views to a philosopher. The (...) essay argues that we should not be misled by the intentionalist fallacy into looking for order within a text as opposed to order commentators can impose by making a philosopher's inconsistencies intelligible. (shrink)

Since the pioneering work of [Aglioti, S., DeSouza, J. F., & Goodale, M. A. . Size-contrast illusions deceive the eye but not the hand. Current Biology, 5, 679–685] visual illusions have been used to provide evidence for the functional division of labour within the visual system—one system for conscious perception and the other system for unconscious guidance of action. However, these studies were criticised for attentional mismatch between action and perception conditions and for the fact that grip size (...) is not determined by the size of an object but also by surrounding obstacles. Stoettinger and Perner [Stoettinger, E., & Perner, J., . Dissociating size representations for action and for conscious judgment: Grasping visual illusions without apparent obstacles. Consciousness and Cognition, 15, 269–284] used the diagonal illusion controlling for the influence of surrounding features on grip size and bimanual grasping to rule out attentional mismatch. Unfortunately, the latter objective was not fully achieved. In the present study, attentional mismatch was avoided by using only the dominant hand for action and for indicating perceived size. Results support the division of labour: Grip aperture follows actual size independent of illusory effects, while finger-thumb span indications of perceived length are clearly influenced by the illusion. (shrink)

Descartes held that it is impossible to make true statements about what we perceive, but I go over alleged cases of illusory experience to show why such a skeptical conclusion (and recourse to God) is overblown. The overreaction, I contend, stems from an insufficient awareness of the habitual expectations brought to any given experience. These expectations manifest themselves in motor terms, as perception constantly prompts and updates an embodied posture of readiness for what might come next. Such habitual (...) anticipations work best when they efface themselves, so it is easy to blame perception when our expectations get frustrated. I illustrate this misdirected blame with the example of a stick partially in water: it is only because we expect the stick to be straight that its appearance as bent is deemed problematic. I thus conclude that, if we factor in the habitual interpretations operative in perception and switch to a processual view that allows practical engagement, we can deflate the worries that led Descartes to rule out perceptual truths. Distancing myself from the naïve “sign” of folk semiotics, my critique draws inspiration from the triadic semiotic model developed in some late medieval schools of Portugal. (shrink)

Size perception of visual objects is highly context dependent. Here we report a novel perceptual size illusion that the self-face, being a unique and distinctive self-referential stimulus, can enlarge its perceived size. By using a size discrimination paradigm, we found that the self-face was perceived as significantly larger than the other-face of the same size. This size overestimation effect was not due to the familiarity of the self-face, since it could be still observed when the self-face was directly compared (...) with a famous face. More crucially, such illusion effect could be extended to a new cartoon face that was transiently associated with one's own face and could also exert further contextual influences on visual size perception of other objects. These findings together highlight the role of self-awareness in visual size perception and point to a special mechanism of size perception tuned to self-referential information. (shrink)

The perception of brightness differences in Ehrenstein figures and of illusory contours in phase-shifted line gratings was investigated as a function of the contrast polarity of the inducing elements. We presented either continuous lines or line-like arrangements composed of aligned dashes or dots whose spacing was varied. A yes/no procedure was used in which naive observers had to decide whether or not they perceived a brightness difference in a given Ehrenstein figure or an illusory contour in a (...) phase-shifted line grating. The results show that brightness differences are perceived to some extent in Ehrenstein figures with inducers of opposite polarity of contrast; however, the percentage of yes response was systematically lower and response times were longer than for figures with inducers of the same polarity. Phase-shifted line gratings with lines of opposite polarity of contrast yielded stronger illusory contours and shorter response times than those with lines of the same polarity. When the sign of contrast was not the same within a given line of induction, neither differences in brightness nor illusory contours were perceived. The results suggest that the mechanisms that lead to apparent differences in brightness are more sensitive to input of the same contrast polarity, the mechanisms generating illusory contours more sensitive to input of opposite polarity. The data are discussed in the light of a multistage approach to illusory form perception and some implications for cortical models of illusory contour integration are discussed. (shrink)

In the abstract the word “self-location” is repeated twice. The second “self-location” was meant to be “self-identification”. The correct sentence reads below:This has recently been tested experimentally in healthy subjects showing that integration of multisensory bodily signals from the entire body with respect to the three aspects: self-location, first-person perspective, and self-identification, is crucial for bodily self-consciousness.

Transcranial magnetic stimulation (TMS) of the visual cortex can induce phosphenes as can non-diagnostic ultrasound, the latter while participants have closed their eyes during Stimulation. Here we sought to study potential alteration of a visual target (a white crosshair) due to application of diagnostic ultrasound to the visual cortex. We applied a randomized series of actual or sham diagnostic ultrasound to the visual cortex of healthy participants while they stared at a visual target, with the ultrasound device placed where TMS (...) elicited phosphenes. These participants observed percepts 7 out of 10 times, consisting of extra or extensions of lines relative to the original crosshair, and additional colors. Observation of a percept occurred an average of 53.7 +/- 2.6% of the time over the course of the experiment for these participants. In contrast, 7 out of 10 participants exposed to sham-only diagnostic ultrasound observed comparable percepts an average of 36.3 +/ 1.9% of the time, a statistically significant difference (p < 0.00001). Moreover, on average, participants exposed to a combination of sham and actual ultrasound reported a net increase of 47.9 percentage points in the likelihood that they would report a visual effect by the end of the experiment. Our experiment demonstrated that a random combination of sham-only and actual diagnostic ultrasound applied to the visual cortex of participants increased the likelihood that they would observe visual effects, but not the type of effects, with that likelihood increasing over the course of the experiment. From this we conclude that repeated exposures by diagnostic ultrasound made the visual cortex more responsive to stimulation of their visual cortex by the visual target. These observations, consistent with other’s observation of effects of diagnostic ultrasound stimulation of human motor cortex and amygdala, as well as the FDA approved nature of diagnostic ultrasound, may lead to increased study of diagnostic ultrasound applied to human brain. (shrink)

The major theoretical framework relative to the perception of illusory figures is reviewed and discussed in the attempt to provide a unifying explanatory account for these phenomena.

Light increment thresholds were measured on either side of one of the illusory contours of a white-on-black Kanizsa square and on the illusory contour itself. The data show that thresholds are elevated when measured on either side of the illusory border. These elevations diminish with increasing distance of the target spot from the white elements which induce the illusory figure. The most striking result, however, is that threshold elevations are considerably lower or even absent when the (...) target is located on the illusory contour itself. At an equivalent position in a control figure where no illusory contour is visible, such a threshold decrease does not occur. The present observations add empirical support to neural theories of illusory form perception. (shrink)

Results from three experiments using spatial forced-choice techniques show that an illusory contour improves the detectability of a spatially superimposed, 1pixel-thin subthreshold line of either contrast polarity. Furthermore, the subthreshold line is found to enhance the visibility of an illusory contour bridging the gap between the two colinear edges of physically defined boundaries. Stimuli which do not induce illusory contours, but reduce uncertainty about the spatial position of the line, give rise to a slight detection facilitation, but (...) the threshold of 75% correct responses is not attained. The data indicate that superimposing illusory contours and 1pixel thin subthreshold lines produces interactions which are similar to classic subthreshold summation. This provides psychophysical evidence for the functional equivalence of illusory and real lines, as suggested by neurophysiological data from single-cell recordings in V1 and V2 of cats and primates. (shrink)

The perceived strength of darkness enhancement in the centre of surfaces surrounded or not surrounded by illusory contours was investigated as a function of proximity of the constituent elements of the display and their angular size. Magnitude estimation was used to measure the perception of the darkness phenomenon in white-on-grey stimuli. Darkness enhancement was perceived in both types of the stimuli used, but more strongly in the presence of illusory contours. In both cases, perceived darkness enhancement increased (...) with increasing proximity of the constituent parts of the display and with their angular size. These results suggest that the occurrence of darkness (or brightness) enhancement phenomena in the centre of the displays is not directly related to illusory contours, which only reinforce the subjective surface brightness/darkness. (shrink)

It has been hypothesized that illusory agency detection is at the basis of belief in supernatural agents and paranormal beliefs. In the present study a biological motion perception task was used to study illusory agency detection in a group of skeptics and a group of paranormal believers. Participants were required to detect the presence or absence of a human agent in a point-light display. It was found that paranormal believers had a lower perceptual sensitivity than skeptics, which (...) was due to a response bias to ‘yes’ for stimuli in which no agent was present. The relation between paranormal beliefs and illusory agency detection held only for stimuli with low to intermediate ambiguity, but for stimuli with a high number of visual distractors responses of believers and skeptics were at the same level. Furthermore, it was found that illusory agency detection was unrelated to traditional religious belief and belief in witchcraft, whereas paranormal beliefs were strongly related to illusory agency detection. These findings qualify the relation between illusory pattern perception and supernatural and paranormal beliefs and suggest that paranormal beliefs are strongly related to agency detection biases. (shrink)

According to the conceptualist view in the philosophy of perception, we possess concepts for all the objects, properties, and relations which feature in our experiences. Richard Heck has recently argued that the phenomenon of illusory experience provides us with conclusive reasons to reject this view. In this paper, I examine Heck’s argument, I explain why I think that Bill Brewer’s conceptualist response to it is ineffective, and I then outline an alternative conceptualist response which I myself endorse. My (...) argument turns on the fact that both Heck, in constructing his objection to conceptualism, and Brewer, in responding to it, miss a crucial distinction between perceptual demonstrative concepts of objects, on the one hand, and perceptual demonstrative concepts of properties, on the other. (shrink)

Philosophical theories of perception are generally admitted to be responses to certain problems or puzzles allied to the ancient dichotomy between Appearance and Reality. For they have been mainly provoked by the incompatibility of the common–sense assumption that an external, physical world exists and is revealed to the senses with the well–known facts of perceptual variation and error. If only what is real were perceived just as if only what is right were done it is possible that many of (...) those questions would never have been asked which lead to moral philosophy and a metaphysics of the external world. But sense perceptions of the same object vary so that it appears to have contradictory qualities and are sometimes completely deceptive. Nor do illusory differ internally from veridical perceptions. Moreover, perceptual variation and error can be unmasked only by such procedures as looking more carefully, listening harder, trying to touch, asking others, in short by more sense experience. So the senses are, as it were, both accused and judge in these disputes and why should a venal judge be trusted more than the criminal he tries? Such “correction” of one experience by another of the same kind seems no more reliable than the original “error.” Philosophers have found all this very puzzling. (shrink)

There is little doubt that we perceive the world as tensed—that is, as consisting of a past, present and future each with a different ontological status—and transient—that is, as involving a passage of time. We also have the ability to execute precisely timed behaviors that appear to depend upon making correct temporal judgments about which changes are truly present and which are not. A common claim made by scientists and philosophers is that our experiences of entities enduring through transient changes (...) are illusory and that our apparently accurately timed behaviors do not reflect dynamical time. We argue that our experiences of objects enduring through transient changes need not be thought of as illusory even if time is not dynamic at the fundamental level of reality. For, the dynamic properties we experience objects as having need not be fundamental properties. They could be weakly emergent from static, temporal properties. Temporal properties, on this view, are similar to ordinary properties like that of being solid, which are correctly experienced as properties of medium-sized material bodies even though they are not instantiated at the fundamental level of reality. (shrink)

Some of the basic terminology of Yogācāra philosophy needs reevaluation. Whereas commentaries almost universally gloss the term dvaya ('duality') with some version of the phrase grāhya grāhaka ca (lit. 'grasped and grasper', but usually translated as 'subject and object'), in fact this gloss is absent from the earliest strata. The term and its gloss are derived from separate streams of Yogācāra reasoning - one from discussions of linguistic conceptualization and the other from discussions of perception. Once we see that (...) these two are distinct, it becomes clear that the commentarial literature asserts their identity in order to philosophically unify Yogācāra thought. One upshot of this is that even in this later assertion 'duality' refers not to the distinction between internal and external reality (as in 'textbook' Yogācāra), but to the falsely projected distinction between mental subjects and mental objects. (shrink)

A mechanistic explanation is a desired outcome in many studies of perception. Such explanations require discovering the processes that contribute to the realization of a perceptual phenomenon at different levels of information processing. The present analysis aims at investigating the obstacles to develop such mechanistic explanations and their potential solutions in the context of psychopathology. Geometric-Optical Illusions (GOIs) are among perceptual phenomena that have been studied to understand psychopathology in various clinical populations. In the present analysis, the GOIs will (...) be discussed as a methodological tool in the investigation of the mechanistic approach to understanding perception in such populations. I will argue that the fact that most such studies are mainly focused on the investigation of susceptibility to GOIs can only lead to classifying such phenomena or to reporting some correlations between different aspects of such phenomena with certain brain activities, without formulating a mechanistic explanation. The investigation of the variables that mediate perceptual phenomena at earlier stages of information processing is required for the formulation of such explanations. Thus, the objective of the present analysis is twofold: 1) showing how ignoring such variables have prevented the formulation of mechanistic explanations of responses to GOIs in clinical populations, such as schizophrenia and autism, 2) analyzing the methodological aspects of an effective approach in which a top-down guidance based on phenomenological insights (the first-person data) along with the insights provided by the existing theories help overcome obstacles in developing mechanistic explanations of GOIs. (shrink)

The subject of the study is color symbolism in F. Fitzgerald’s novel «The Great Gatsby» in the aspect of an ambivalent understanding of the conceptual solution in the use of a certain color in creating images of characters, in describing the setting and semantic content of the ideological content of the work and its screen interpretations. The object of study is color as a meaning-forming concept in literature and cinema, the symbolism of color. The work of Francis S. Fitzgerald «The (...) Great Gatsby» is of interest in the study of the influence of color palette. The main research methods are analytical and comparative historical. The color concepts of F. S. Fitzgerald's book “The Great Gatsby” and film adaptations are comprehended. This work by F. S. Fitzgerald is of interest to the modern Russian reader and viewer due to the fact that the problems raised in the novel are still relevant today. The writer touches on the popular theme of the American dream in literature and cinema. The story of the main characters is a vivid example of the illusory nature of this dream, and the lifestyle of the characters and their worldview demonstrate spiritual emptiness and cold indifference to everything except money and wealth. The scientific novelty of the article lies in the study of the ambivalence of perception of the coloristic solution of the images of characters in the book in comparison with its screen interpretations. The author comes to the conclusion that F. S. Fitzgerald in the novel «The Great Gatsby» uses a color palette in creating images of characters and describing the scene in such a way that the ambiguity in the perception of color most unexpectedly and sharply emphasizes the problems raised and becomes the basis for rethinking the ideological content of the work. (shrink)

Investigating the influence of perception on the control of visually guided action typically involves controlled experimentation within the laboratory setting. When appropriate, however, behavioral research of this nature may benefit from the use of methods that allow for remote data collection outside of the lab. This study tested the feasibility of using remote data collection methods to explore the influence of perceived target size on visually guided cursor movements using the Ebbinghaus illusion. Participants completed the experiment remotely, using the (...) trackpad of their personal laptop computers. The task required participants to click on a single circular target presented at either the left or right side of their screen as quickly and accurately as possible, or to emphasize speed or accuracy. On each trial the target was either surrounded by small or large context circles, or no context circles. Participants’ judgments of the targets’ perceived size were influenced by the illusion, however, the illusion failed to produce differences in click-point accuracy or movement time. Interestingly, the illusion appeared to affect participants’ movement of the cursor toward the target; more directional changes were made when clicking the Perceived Large version of the illusion compared to the Perceived Small version. These results suggest the planning of the cursor movement may have been influenced by the illusion, while later stages of the movement were not, and cursor movements directed toward targets perceived as smaller required less correction compared to targets perceived as larger. (shrink)

This paper examines Milner and Goodale’s hypothesis about the two visual streams and raises the questions of whether properties in egocentric space (commonly associated with the vision-for-action, or "dorsal," stream) can be part of the phenomenal content of perceptual experience, or only properties in allocentric space (commonly associated with the vision-for-perception, or "ventral," stream) can play this role, and how (if at all) properties in egocentric space differ from properties in allocentric space. These questions are reminiscent of issues raised (...) by Christopher Peacocke's "equal-sized trees" case: if you are looking at equal-sized trees on the side of a road, the trees will phenomenally look to you to be equally tall. But it is also true that a tree will take up more of the space in your visual field the closer it is to you. So, the equal-sized trees will also phenomenally look to you to have different heights. Your (visual) perceptual experience is not illusory. That is, the trees veridically look to you to have the same height, and they also veridically look to you to have different heights. Call the sort of issue raised here the "problem of dual looks." I provide a solution to the problem of dual looks that helps shed light on whether properties in egocentric space can be part of the phenomenal content of perceptual experience, and how (if at all) properties in egocentric space differ from properties in allocentric space. (shrink)

In visual science the term filling-inis used in different ways, which often leads to confusion. This target article presents a taxonomy of perceptual completion phenomena to organize and clarify theoretical and empirical discussion. Examples of boundary completion (illusory contours) and featural completion (color, brightness, motion, texture, and depth) are examined, and single-cell studies relevant to filling-in are reviewed and assessed. Filling-in issues must be understood in relation to theoretical issues about neuralignoring an absencejumping to a conclusionanalytic isomorphismCartesian materialism, a (...) particular neural stage that forms the immediate substrate of perceptual experience enactiveanimatesubpersonal” considerations about internal processing, but rather by considerations about the task of vision at the level of the animal or person interacting with the world. (shrink)

By analyzing descriptions of illusory and nonillusory figures, Richer called into question the common assumption that illusory and nonillusory perceptions were experientially the same and differed only in terms of their accuracy. The present study attempted to replicate Richer's work with a focus on identifying within the subjects' descriptions any orienting attitudes corresponding to these two forms of perception. Nineteen student volunteers were asked to describe two illusory figures and a nonillusory control of similar complexity. The (...) descriptions revealed consistent differences between the two forms. However, the Hering and Zollner figures were not always described in illusory terms, and surprisingly, several subjects described the control as if it were illusory. Further, perceptual accuracy was not guaranteed by nonillusory experience. Subjects described the figures from within one of three different orienting attitudes-atomizing, representational, and geometrical-organizing. The latter attitude appeared necessary for the phenomena of illusory perception and experience. Though the present findings confirmed Richer's distinction between illusory and nonillusory experience, they also indicate the need for further differentiation- illusory perception versus illusory experience. Finally, the findings also supported Luria's and Segall, Campbell, and Herskovits's position on the importance of particular cultural and educational experiences and codes in relation to perceptual illusions. (shrink)