Moon illusion in pictures: a multimechanism approach

The existence of the moon illusion in pictorial representations was demonstrated in 6 experiments. Ss either judged the size of the moon in pictures, depicted as on the horizon or high in the sky, or drew horizon and elevated moons. The horizon moon was consistently judged to be larger than the elevated moon, independent of the angle at which the pictures are viewed. The distance paradox usually observed with the moon illusion (horizon moon apparently closer than the elevated moon) also exists in pictures. The magnitude of both size and distance effects depends on the salience of depicted depth cues. The pattern of results suggests that the moon illusion is caused by several interacting mechanisms and that use of pictorial stimuli may allow the separation of various cognitive from physiological contributions to the illusion.     

Feeling darkness: a visually induced somatosensory illusion

Although the five primary senses have traditionally been thought of as separate, examples of their interactions, as well as the neural substrate possibly underlying them, have been identified. Arm position sense, for example, depends on touch, proprioception, and spatial vision of the limb. It is, however, unknown whether position sense is also influenced by more fundamental, nonspatial visual information. Here, we report an illusion that demonstrates that the position sense of the eyelid partly depends on information regarding the relative illumination reported by the two eyes. When only one eye is dark-adapted and both eyes are exposed to a dim environment, the lid of the light-adapted eye feels closed or "droopy." The effect decreases when covering the eye by hand or a patch, thus introducing tactile information congruent with the interocular difference in vision. This reveals that the integration of vision with touch and proprioception is not restricted to higher-level spatial vision, but is instead a more fundamental aspect of sensory processing than has been previously shown.     

Perisaccadic parietal and occipital gamma power in light and in complete darkness

Our objective was to determine perisaccadic gamma range oscillations in the EEG during voluntary saccades in humans. We evaluated occipital perisaccadic gamma activity both in the presence and absence of visual input, when the observer was blindfolded. We quantified gamma power in the time periods before, during, and after horizontal saccades. The corresponding EEG was evaluated for individual saccades and the wavelet transformed EEG averaged for each time window, without averaging the EEG first. We found that, in both dark and light, parietal and occipital gamma power increased during the saccade and peaked prior to reaching new fixation. We show that this is not the result of muscle activity and not the result of visual input during saccades. Saccade direction affects the laterality of gamma power over posterior electrodes. Gamma power recorded over the posterior scalp increases during a saccade. The phasic modulation of gamma by saccades in darkness--when occipital activity is decoupled from visual input--provides electrophysiological evidence that voluntary saccades affect ongoing EEG. We suggest that saccade-phasic gamma modulation may contribute to short-term plasticity required to realign the visual space to the intended fixation point of a saccade and provides a mechanism for neuronal assembly formation prior to achieving the intended saccadic goal. The wavelet-transformed perisaccadic EEG could provide an electrophysiological tool applicable in humans for the purpose of fine analysis and potential separation of stages of 'planning' and 'action'.     

Spatial configurations: Erikson reexamined

In a 1951 study, Erik Erikson reported differences in preadolescents' play constructions. He claimed that his findings reflected differences between males and females in their experience and perception of space. The present study replicated but also expanded the original design. In order to control for possible sex bias of materials, a constructed scene using only blocks was added to Erikson's original design. The results failed to replicate Erikson's findings. In fact, in the construction of scenes from blocks, more females than males built erected structures; this was true across all ages. These findings are in direct contrast to Erikson's results, and they lead to the conclusion that the materials provided, not innate anatomical sex differences, account for the resulting spatial configurations.The research reported here was part of the first author's dissertation. The authors gratefully acknowledge the cooperation of Holy Innocents Episcopal School and Georgia State University.     

The solitaire illusion: An illusion of numerosity

A new illusion in which the apparent number of elements of two kinds is determined by their spatial arrangement is described. The illusion is such that one large cluster appears to contain more elements than several small clusters, clustering being determined by Gestalt principles. The illusion was found both in adults and in children of 8 years.     

Absorption and hypnotizability: context effects reexamined

Two independent studies failed to find evidence consistent with Council, Kirsch, and Hafner (1986), who argued that the repeatedly observed correlations between Tellegen's (1981) Absorption Scale (TAS) and hypnosis measures were artifacts of testing context, and de Groot, Gwynn, and Spanos (1988), who claimed evidence for a Gender x Context moderator effect. In the present studies, Ss completed the TAS and other personality questionnaires on 2 occasions: during an independent survey and later immediately prior to an assessment of hypnotizability. In Experiment 1 (N = 475), the effect of context on the relation between questionnaire scores and hypnotizability was weak and variable; in Experiment 2 (N = 434), these weak effects were reversed. The results reaffirm the construct validity of absorption as both a major dimension of personality and as a predictor of hypnotic responsiveness.     

The peripheral drift illusion: a motion illusion in the visual periphery

Circularly repeating patches containing sawtooth luminance gradients produce a sensation of motion when viewed in the periphery. Illusory motion is perceived in a dark-to-light direction, but only when one's gaze is directed to different locations around the stimulus, a point outside the display is fixated and the observer blinks, or when the stimulus is sequentially displayed at different locations whilst the observer fixates one point. We propose that the illusion is produced by the interaction of three factors: (i) introducing transients as a result of eye movements or blinks; (ii) differing latencies in the processing of luminance; and (iii) spatiotemporal integration of the differing luminance signals in the periphery.     

The generation effect in primed word-fragment completion reexamined

Summary Two experiments were designed to test a claim made by Gardiner (1988) that there are generation effects in implicit memory as measured by word-fragment completion. Subjects either read words at study or generated the words from fragments. As in previous research, fragments were completed to a greater extent if they were identical at study and test than if they differed. In Experiment 1 it was found that subjects could recognize explicitly the exact form of fragments that had been used for self-generation and distinguish these from other forms of fragments. An analysis of the contingency relations between recognition of fragments and fragment completion showed a high degree of dependence between the two tests. In Experiment 2 it was found that the match of surface features between study and test was a necessary, but not sufficient, condition to produce enhancement of priming. The results are interpreted as supporting the claim that generation does involve a data-driven component in addition to semantic elaboration.This research was supported by a grant from the Swedish Council for Research in the Humanities and Social Sciences to Lars-Göran Nilsson.     

Spatial limits on the nonvisual self-touch illusion and the visual rubber hand illusion: Subjective experience of the illusion and proprioceptive drift

The nonvisual self-touch rubber hand paradigm elicits the compelling illusion that one is touching one’s own hand even though the two hands are not in contact. In four experiments, we investigated spatial limits of distance (15 cm, 30 cm, 45 cm, 60 cm) and alignment (0°, 90° anti-clockwise) on the nonvisual self-touch illusion and the well-known visual rubber hand illusion. Common procedures (synchronous and asynchronous stimulation administered for 60 s with the prosthetic hand at body midline) and common assessment methods were used. Subjective experience of the illusion was assessed by agreement ratings for statements on a questionnaire and time of illusion onset. The nonvisual self-touch illusion was diminished though never abolished by distance and alignment manipulations, whereas the visual rubber hand illusion was more robust against these manipulations. We assessed proprioceptive drift, and implications of a double dissociation between subjective experience of the illusion and proprioceptive drift are discussed.     

Daylight and darkness: Images of Christians in mixed marriages

Marriage between Christians and non-Christians has generally been regarded with suspicion by the churches, and has at times been severely punished. However, mixed marriage has also sometimes been seen as a means by which the non-Christian partner may be drawn into the faith. In this article I review some of the underlying reasons for these attitudes and the theological concepts of marriage which informed those responsible for its regulation. I focus particularly on the issues and images surrounding religious intermarriage in the early Church and during the medieval period, with special reference to legends and literature.     

The fluttering-heart illusion: a new hypothesis

The fluttering-heart illusion is a perceived lagging behind of a colour target on a background of a different colour when the two are oscillated together. It has been proposed that the illusion is caused by a differential in the perceptual latencies of different colours (Helmholtz 1867/1962), a differential in rod-cone latencies (von Kries 1896) and rod-cone interactions (von Grünau 1975, 1976 Vision Research 15 431-436, 437-440; 16 397-401; see list of references there). The purpose of this experiment was to assess the hypothesis that the fluttering-heart illusion is caused by a differential in the perceived velocities of chromatic and achromatic motion. To evaluate this hypothesis, we tested observers possessing normal colour vision and deuteranopes. The perceived delay of a chromatic target relative to an achromatic target was measured as a function of background cone contrast and target colour. For observers with normal colour vision, the perceived delay of the chromatic target is greater in the L-S than the L-M testing conditions. The reverse is observed in deuteranope observers. We suggest that this is caused by the absence of an L-M opponent mechanism contributing to chromatic motion in deuteranopes. Greater background cone contrasts tended to yield smaller perceived delays in both normal and deuteranope observers, indicating that greater chromatic modulation decreases the perceived delay of the colour target. These results support the hypothesis that the fluttering-heart illusion can be explained by a differential in the perceived velocities of chromatic and achromatic motion.     

Reading aloud polysyllabic words and nonwords: The syllabic length effect reexamined

Two experiments were run in order to reinvestigate the role of the number of syllables in naming. Experiment 1 (word naming) showed that effects of number of syllables on naming latency were observed for very low-frequency words but not for high-frequency words (thus replicating Jared & Seidenberg’s, 1990, finding). In Experiment 2 (nonword naming), syllabic length effects were also obtained for nonwords. Control experiments found no effect on the latency of delayed naming of the same words and nonwords. These results suggest that naming does require syllabic decomposition, at least for very low-frequency words and nonwords in French. In particular, these data are compatible with any model of reading that postulates that reading aloud depends on the activity of two procedures: (1) a procedure that operates in parallel across a letter string (and does not generate a strong syllabic length effect) and that is the predominant process in generating responses to high-frequency words, and (2) another procedure that operates serially across a letter string (and generates a strong syllabic length effect) and that is the predominant process in generating responses to very low-frequency words and nonwords. These results are discussed in the context of the multiple-trace memory model for polysyllabic word naming (Ans, Carbonnel, & Valdois, 1998).     

The real as illusion: deconstructing power in family therapy

This paper examines the current issue of power and intervention in family therapy from the perspective of Jacques Derrida's philosophy. In a deconstructive reading which presents power as both real and socially constructed, it negotiates the border between such dualities as knowing/ not-knowing, intervention/non-intervention, and power/non-power. The paper tracks Goolishian and Anderson's approach to therapy as deconstructive in practice, but not in theory, and discusses a double view of power in relation to both Bateson and Foucault. It suggests that power is both endemic to the context of family therapy and an illusion of epistemology. The paper concludes with a discussion of the wider question of ethics in relation to technology.     

Thatcher illusion: dependence on angle of rotation

The expression of a face with its eyes and mouth inverted changes from 'pleasant' to 'grotesque' as the stimulus is rotated from 180 degrees to 0 degree (Thatcher illusion). We determined the angular orientation at which this change occurred for three manipulated faces. Mean thresholds for eighteen observers were found to lie between 94 degrees and 100 degrees relative to the vertical with an average overlap of about 15 degrees between an observer's ascending and descending thresholds. The sudden nature and relatively narrow zone of the changeover suggest a neuronal step-tuning of hypothetical face cells in the human brain, underlying the holistic ('grotesque') versus componential ('pleasant') processing of upright versus upside-down faces. Findings are discussed within the framework of cognitive, neuroimaging, and single-cell studies.