Perceptual fade-out occurs in the binocularly viewed Ganzfeld.

The conviction that time-varying signals are essential for normal visual perception was recently challenged by Bolanowski and Doty who observed that no 'blankouts' occurred in the binocularly viewed Ganzfeld. They suggested that monocularly perceived fading is caused by the eye in darkness suppressing the non-Ganzfeld-viewing eye. In the present paper, fade-out perception under monocular and binocular Ganzfeld viewing is compared, and the effect of the free eye on the Ganzfeld-viewing eye is tested directly. Results show that fading takes place under both monocular and binocular viewing. The data reenforce the view that transient inputs are necessary for maintaining visual perception. It is also shown that there are two Ganzfeld-related phenomena--fade-out and blackout. Fade-out, a slow gradual loss of brightness and of saturation perception, is observed by all subjects under both monocular and binocular viewing, and is affected by the light intensity and wavelength. It is probably retinal in origin. Blackout, a brief intermittent loss of all visual sensation, is experienced by some subjects in the monocular Ganzfeld only and is not appreciably affected by the light intensity or wavelength. It may be caused by a central blocking of all input to the perceiving stage.     

Reliability and dimensionality of judgments of visually textured materials

We extended perceptual studies of the Brodatz set of textured materials. In the experiments, texture perception for different texture sets, viewing distances, or lighting intensities was examined. Subjects compared one pair of textures at a time. The main task was to rapidly rate all of the texture pairs on a number scale for their overall dissimilarities first and then for their dissimilarities according to six specified attributes (e.g., texture contrast). The implied dimensionality of perceptual texture space was usually at least four, rather than three. All six attributes proved to be useful predictors of overall dissimilarity, especially coarseness and regularity. The novel attribute texture lightness, an assessment of mean surface reflectance, was important when viewing conditions were wide-ranging. We were impressed by the general validity of texture judgments across subject, texture set, and comfortable viewing distances or lighting intensities. The attributes are nonorthogonal directions in four-dimensional perceptual space and are probably not narrow linear axes. In a supplementary experiment, we studied a completely different task: identifying textures from a distance. The dimensionality for this more refined task is similar to that for rating judgments, so our findings may have general application.     

Determinants of stability in the perception of subjective contour

The present study constituted an initial experimental effort to examine the fragmentation characteristics of subjective contours within the photopic and upper 5cotopic ranges of illumination. Four stimulus factors known to influence the visibility of subjective contours—target luminance, inducing area size and contrast, and contour orientation—were examined. Results indicated that subjective contours are indeed unstable perceptual phenomena. On the average, fragmentation or fading occurred after only 15 sec of observation, and some farm of stimulus outage was present for 28% of the viewing time of each stimulus. Fragmentation latency was significantly shorter and total time in fragmentation longer for diamond than for square contours, and total time in fragmentation varied inversely with inducing-area size. Fragmentation tendedto occur in whole units rather than in isolated elements, a result reminiscent of the fading of real Contours under impoverished viewing conditions.     

Prenatal experience and postnatal perceptual preferences: evidence for attentional-bias in bobwhite quail embryos (Colinus virginianus)

Previous studies have indicated that concurrent multimodal sensory stimulation can interfere with prenatal perceptual learning. This study further examined this issue by exposing 3 groups of bobwhite quail embryos (Colinus virginianus) to (a) no supplemental stimulation, (b) a bobwhite maternal call, or (c) a maternal call paired with a pulsating light in the period prior to hatching. Experiments differed in terms of the types of stimuli presented during postnatal preference tests. Embryos receiving no supplemental stimulation showed no preference between stimulus events in all testing conditions. Embryos receiving exposure to the unimodal maternal call preferred the familiar call over an unfamiliar call regardless of the presence or absence of pulsating light during testing. Embryos exposed to the call-light compound preferred the familiar call only when it was paired with the light during testing. These results suggest that concurrent multimodal stimulation does not interfere with prenatal perceptual learning by overwhelming the young organism's limited attentional capacities. Rather, multimodal stimulation biases what information is attended to during exposure and subsequent testing.     

Grouping effects in flash-induced perceptual fading

We show that the flash-induced fading effect can be influenced by grouping based on colour and shape similarity. In flash-induced fading, peripherally presented elements perceptually disappear after a flash has been presented around or next to the element(s) (Kanai and Kamitani, 2003 Journal of Cognitive Neuroscience 15 664-672). In the present study, two elements (which could either be similar or different in both colour and shape) were presented at an eccentricity of 2.6 degrees from a fixation cross. After 2 s, a short flash (40 ms) was presented around one of the elements. The two elements remained on the screen for 2.5 s after the flash. We found a higher percentage of mutual perceptual disappearance when the two elements were similar in colour or in shape. These results converge with other findings showing that perceptual fading phenomena are influenced by effects of perceptual grouping. This indicates that, besides low-level adaptation, more global processes play a part in perceptual fading as well and should thus be taken into account in giving a full explanation of perceptual fading in general.     

Attention and Brain Activity While Watching Television: Components of Viewer Engagement

Television commercials include elements designed to engage the viewer's attention. Manipulations of the commercial's visual structure that result in rapid pacing or frequent scene changes can be engaging because they require a frequent redirection of visual attention. Manipulations of semantic content through such techniques as the inclusion of humorous or anomalous elements can elicit cognitive engagement. Structural manipulations in videos are known to attenuate the alpha (8 to 13 Hz) rhythm of the electroencephalogram (EEG) recorded over posterior cortical regions involved with visual processes. To examine whether other engaging elements also affect the alpha rhythm, EEG was recorded from 10 participants who viewed television commercials. Principal components analysis was used to decompose the alpha rhythm into underlying factors that varied in spatial topography over the head and in spectral composition. Across commercials, the power of a posterior-distributed alpha component was inversely correlated with the frequency of scene changes. In contrast, a frontal component in the lower frequency portion of the alpha band was attenuated during commercials that elicited high subjective interest, independent of scene change frequency. And, an upper-frequency frontal alpha component was attenuated during commercials for which the item being advertised had a high probability of being subsequently recalled, independent of other factors. These frontal patterns of alpha reactivity are consistent with other neuroimaging results concerning frontal lobe activation by executive processes and episodic memory encoding. With appropriate neurologically guided analysis, EEG signals can provide a unique means of monitoring both perceptual and higher order neurocognitive processes during television viewing.     

A qualitative analysis of sensory phenomena induced by perceptual deprivation

Previous studies have shown that misperceptions and illusory experiences can occur if sensory stimulation is withdrawn or becomes invariant even for short periods of time. Using a perceptual deprivation paradigm, we created a monotonous audiovisual environment and asked participants to verbally report any auditory, visual or body-related phenomena they experienced. The data (analysed using a variant of interpretative phenomenological analysis) revealed two main themes: (1) reported sensory phenomena have different spatial characteristics ranging from simple percepts to the feeling of immersion in a complex multisensory environment and (2) the active contribution of the perceiver where participants report engaging in exploratory processes even when there is nothing to find. Detailed analysis of the qualitative data further showed that participants who reported more perceptual phenomena were more likely to report internal bodily sensations, move more during the experiment and score higher on the Revised Hallucination Scale than those reporting fewer percepts explicitly linking perceptual deprivation to somatic phenomena. The results demonstrate how the variety of sensory experiences induced by perceptual deprivation can give further insight into the factors mediating conscious awareness and may suggest ways in which the brain imposes meaning on the environment under invariant sensory conditions.     

Lifespan differences in nonlinear dynamics during rest and auditory oddball performance

Electroencephalographic recordings (EEG) were used to assess age-associated differences in nonlinear brain dynamics during both rest and auditory oddball performance in children aged 9.0-12.8 years, younger adults, and older adults. We computed nonlinear coupling dynamics and dimensional complexity, and also determined spectral alpha power as an indicator of cortical reactivity. During rest, both nonlinear coupling and spectral alpha power decreased with age, whereas dimensional complexity increased. In contrast, when attending to the deviant stimulus, nonlinear coupling increased with age, and complexity decreased. Correlational analyses showed that nonlinear measures assessed during auditory oddball performance were reliably related to an independently assessed measure of perceptual speed. We conclude that cortical dynamics during rest and stimulus processing undergo substantial reorganization from childhood to old age, and propose that lifespan age differences in nonlinear dynamics during stimulus processing reflect lifespan changes in the functional organization of neuronal cell assemblies.     

Is the anisotropy of perceived 3-D shape invariant across scale?

A number of studies have resulted in the finding of a 3-D perceptual anisotropy, whereby spatial intervals oriented in depth are perceived to be smaller than physically equal intervals in the frontoparallel plane. In this experiment, we examined whether this anisotropy is scale invariant. The stimuli were L shapes created by two rods placed flat on a level grassy field, with one rod defining a frontoparallel interval, and the other, a depth interval. Observers monocularly and binocularly viewed L shapes at two scales such that they were projectively equivalent under monocular viewing. Observers judged the aspect ratio (depth/width) of each shape. Judged aspect ratio indicated a perceptual anisotropy that was invariant with scale for monocular viewing, but not for binocular viewing. When perspective is kept constant, monocular viewing results in perceptual anisotropy that is invariant across these two scales and presumably across still larger scales. This scale invariance indicates that the perception of shape under these conditions is determined independently of the perception of size.     

Viewing instructions impact emotional memory differently in older and young adults

The current study examines how the instructions given during picture viewing impact age differences in incidental emotional memory. Previous research has suggested that older adults' memory may be better when they make emotional rather than perceptual evaluations of stimuli and that their memory may show a positivity bias in tasks with open-ended viewing instructions. Across two experiments, participants viewing photographs either received open-ended instructions or were asked to make emotionally focused (Experiment 1) or perceptually focused (Experiment 2) evaluations. Emotional evaluations had no impact on older adults' memory, whereas perceptual evaluations reduced older adults' recall of emotional, but not of neutral, pictures. Evidence for the positivity effect was sporadic and was not easier to detect with open-ended viewing instructions. These results suggest that older adults' memory is best when the material to be remembered is emotionally evocative and they are allowed to process it as such.     

The effects of binocular and motion-generated information on the perception of depth and height

The perception of distance and size in the presence of optical gradient information was investigated under four viewing conditions—binocular view with and without head motion, and monocular view with and without head motion. Subjects (60 adults) matched distance intervals (from 15 to 127 cm) and heights of a target triangle (from 5 to 15 cm) by adjusting the length of a metal tape. Both linear and power functions were fitted to each individual’s distance judgments, and the competing perceptual models were compared. For both models, it was found that binocular information was sufficient to specify relative, but not absolute, distance, that monocular information was sufficient to specify an orderly relation between target distance and judgment but not absolute distance, that average error was less in the binocular conditions, and that perceived distance was not affected in either condition by the addition of head motion. The analysis of size judgments revealed that monocular and binocular judgments did not differ, that matches made with and without head motion did not differ, and that, in all conditions, matches exceeded target heights by an average 30% to 40%. Judged size was also analyzed as a function of target distance. In all conditions but monocular view with head motion, the effect of distance was to increase size judgments. The distance judgments support the hypothesis (Purdy, 1958) that the binocular stimulus carries information that the monocular stimulus does not; they fail to support the hypothesis (Gibson, 1966) that observer motion adds information to the static stimulus. The size judgments support neither hypothesis but suggest an independence of perceived size from perceived distance.     

Perceptual categorization in the cerebral hemispheres

The suggestion of a functional hemispheric dissociation in performing perceptual categorization was examined in two tachistoscopic experiments with normal adults. Subjects were required to match physically identical or similar, but nonidentical, pictures of animals. The first experiment showed no hemispheric difference and indicated that both hemispheres could resort to two different types of categorization process as a function of the simultaneous or delayed mode of presentation of the stimuli. In the second experiment, the viewing conditions were manipulated so as to afford a reduced amount of stimulus energy, and a significant left-visual-field advantage was then obtained. The results are discussed with respect to models of information processing in the cerebral hemispheres, and in relation to impairments in object recognition following brain damage.     

汉语双字词句知觉广度的眼动研究

阅读知觉广度通常指阅读者在阅读文本过程中每次注视能获取有用视觉信息的范围。既往的汉语知觉广度的研究一般把单字作为基本的知觉呈现单元,但在某些呈现条件下,此类呈现方式会导致阅读过程中的语义加工的完整性被破坏。本研究采用眼动追踪技术,使用移动窗口范式和中央凹掩蔽范式,使用双字词句作为阅读材料,双字词作为基本的知觉呈现单元,探讨在保证知觉呈现单元语义完整性的基础上大学生的汉语阅读知觉广度。实验一采用移动窗口范式,结果发现,知觉广度范围为注视词左侧1个双字词及右侧1-2个双字词的空间。实验二采用中央凹掩蔽范式,结果验证了实验一的研究结果。该结果表明,在汉语阅读过程中,以双字词为基本的视觉呈现单元,较既往研究中单字为基本呈现单元的情况,更好地保证了阅读中语义的完整性,从而获得了更大的知觉范围。该结果建立于视觉呈现单元的语义完整性的基础上,是对现有的汉语阅读知觉广度理论的完善和扩展。     

Influence of semantic consistency and perceptual features on visual attention during scene viewing in toddlers

Conceptual representations of everyday scenes are built in interaction with visual environment and these representations guide our visual attention. Perceptual features and object-scene semantic consistency have been found to attract our attention during scene exploration. The present study examined how visual attention in 24-month-old toddlers is attracted by semantic violations and how perceptual features (i. e. saliency, centre distance, clutter and object size) and linguistic properties (i. e. object label frequency and label length) affect gaze distribution. We compared eye movements of 24-month-old toddlers and adults while exploring everyday scenes which either contained an inconsistent (e.g., soap on a breakfast table) or consistent (e.g., soap in a bathroom) object. Perceptual features such as saliency, centre distance and clutter of the scene affected looking times in the toddler group during the whole viewing time whereas looking times in adults were affected only by centre distance during the early viewing time. Adults looked longer to inconsistent than consistent objects either if the objects had a high or a low saliency. In contrast, toddlers presented semantic consistency effect only when objects were highly salient. Additionally, toddlers with lower vocabulary skills looked longer to inconsistent objects while toddlers with higher vocabulary skills look equally long to both consistent and inconsistent objects. Our results indicate that 24-month-old children use scene context to guide visual attention when exploring the visual environment. However, perceptual features have a stronger influence in eye movement guidance in toddlers than in adults. Our results also indicate that language skills influence cognitive but not perceptual guidance of eye movements during scene perception in toddlers.     

Affect regulation and food intake in bulimia nervosa: emotional responding to food cues after deprivation and subsequent eating

Emotional responding to salient food cues and effects of food deprivation and consumption were investigated in 32 women with bulimia and 32 control women. One half of each group was food deprived before viewing unpleasant, neutral, pleasant, and food-related pictures. Then participants could eat from a buffet before viewing a parallel picture set. Women with bulimia showed a substantial potentiation of startle responses during viewing of food cues relative to control women. This startle potentiation was attenuated by food deprivation and augmented by increased food consumption. These data support the affective regulation model suggesting that food cues prompt negative affective states in women with bulimia, who are overwhelmed by fasting. The resulting deprivation increases the incentive value of food cues and may thus trigger binge eating.     

Perception of depth: Processing of simple positional disparity as a function of viewing distance

Dependency of perceived depth (relative to the fixation point) on disparity, viewing distance, and the type of the stereoscopic stimulus was investigated. Nearly complete constancy of depth, as required for a veridically matched perception, was observed only at small disparity values and with the larger square-formed stimulus; under these conditions, perceived depth corresponded well with real depth intervals for close viewing distances. Additionally, a model for perceptual processing of both variables, disparity and viewing distance, was applied to the data.     

Top-down effects of semantic knowledge in visual search are modulated by cognitive but not perceptual load

Moores, Laiti, and Chelazzi (2003) found semantic interference from associate competitors during visual object search, demonstrating the existence of top-down semantic influences on the deployment of attention to objects. We examined whether effects of semantically related competitors (same-category members or associates) interacted with the effects of perceptual or cognitive load. We failed to find any interaction between competitor effects and perceptual load. However, the competitor effects increased significantly when participants were asked to retain one or five digits in memory throughout the search task. Analyses of eye movements and viewing times showed that a cognitive load did not affect the initial allocation of attention but rather the time it took participants to accept or reject an object as the target. We discuss the implications of our findings for theories of conceptual short-term memory and visual attention.     

Attention to Television: Alpha Power and Its Relationship to Image Motion and Emotional Content

A laboratory experiment investigated the impact of image motion and emotional content in brief television clips on attention. Using an electroencephalogram (EEG) as a measure of attention, cortical activity in 25 participants was measured while they viewed either still or moving emotion-provoking images. Spectral analysis of the EEG was done to gauge changes in alpha-wave (8-13 Hz) power because reductions in alpha power are thought to indicate greater attention. The analysis revealed that subjective reports of emotional arousal were directly related to cortical activation (i.e., reduced alpha power), and this was particularly true at the parietal recording site. The relationship between alpha power and ratings of valence was curvilinear; cortical activation was associated with both positive and negative images relative to neutral images. Alpha power was also reduced during the viewing of moving compared with still images, and this effect occurred independent of stimulus valence. The association of greater cortical activation with moving than with still images is consistent with previous research using autonomic measures and suggests that image motion modulates emotional responding-and sustains attention-primarily through increasing "gain" in the arousal dimension.     

The eyes in imagery and perceptual processes: first remarks.

Through an echographic system we examined the activity of the crystalline lens of 10 men and women during real perceptual activity and during imagery. Subjects had to perceive near and far stimuli and to imagine reading a word on a page of a book (near imagined stimulus) or seeing a ship on the horizon (far imagined stimulus). Results showed that processes of accommodation (linked to the variations of the optical axis of the crystalline lens) occur in both real and imaginative conditions. The first results suggest an active role of the eye during imagery.     

Perceptual fading without retinal adaptation

A retinally stabilized object readily undergoes perceptual fading and disappears from consciousness. This startling phenomenon is commonly believed to arise from local bottom-up sensory adaptation to edge information that occurs early in the visual pathway, such as in the lateral geniculate nucleus of the thalamus or retinal ganglion cells. Here we use random dot stereograms to generate perceivable contours or shapes that are not present on the retina and ask whether perceptual fading occurs for such "cortical" contours. Our results show that perceptual fading occurs for "cortical" contours and that the time a contour requires to fade increases as a function of its size, suggesting that retinal adaptation is not necessary for the phenomenon and that perceptual fading may be based in the cortex.