Treatment of lymphoid malignancies in patients with ataxia-telangiectasia

The present study tested the idea that if subjects rely more on scene-based pictorial cues when binocular cues are not available, then both their perceptual judgements and their grasp might be influenced by pictorial illusions such as the Ebbinghaus (Titchener) Circles Illusion under monocular viewing conditions. Under binocular viewing conditions, subjects were always able to scale their grip accurately to the true size of the target disc and were unaffected by the illusion. Under monocular viewing, however, subjects appeared to be influenced by the illusion. Thus, when confronted with physically different target discs displayed on backgrounds that made them appear equivalent in size, subjects treated the two discs as equivalent--even when picking them up. These results, combined with earlier work from our laboratory suggests that binocular information plays a critical role in normal human prehension but when this information is not available the visuomotor system is able to "fall back" on the remaining monocular cues, which can cause the visuomotor system to be more susceptible to pictorial illusions.     

Size contrast as a function of conceptual similarity between test and inducers

In four experiments, the effect of the semantic relationship between test and inducing stimuli on the magnitude of size contrast in an Ebbinghaus-type illusion was explored. In Experiments 1 and 2, the greatest illusion was found when test and inducing stimuli were identical in shape and differed only in size. Decreased size contrast was found when inducing stimuli were drawn from the same category as the test stimulus, but were not visually identical. Even less size contrast was found when inducing stimuli were from a near conceptual category, with the least effect when they were drawn from a completely different category. In Experiment 3, it was demonstrated that even if test and inducing stimuli are drawn with identical geometric elements, the size contrast illusion is greatly reduced if they represent apparently different conceptual categories (through the manipulation of orientation and perceptual set). In Experiment 4, any geometric or spatial confounds were ruled out. These results suggest that size contrast is strongly influenced by the conceptual similarity between test and inducing stimuli.     

Dynamic illusion effects in a reaching task: Evidence for separate visual representations in the planning and control of reaching.

The effects of an orientation illusion on perception and 2 different actions were investigated. An 8-cm?×?2-cm cylindrical bar was placed in front of participants at various orientations. A background grating was used to induce an orientation illusion. In a perception task, the illusion affected participants' ability to align the bar with their sagittal planes. In one reaching task, a similar effect of the illusion was found on the choice between 2 possible grasping postures. In a second reaching task involving a single grasping posture, the orientation illusion affected the orientation of the hand at the beginning of the reach but not near its end. The authors argue that reaching trajectories are planned and initiated through a context-dependent representation but are corrected on-line through a context-independent representation. The relation of this model to a more general dichotomy between perception and action is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceiving and tracking kinesthetic stimuli: Further evidence of motor–perceptual interactions.

Two experiments pursued previous studies (P. Viviani & P. Mounoud, 1990; P. Viviani & N. Stucchi, 1989) on motor–perceptual interactions. The right arm of blindfolded participants was moved passively along elliptic trajectories. Kinematics was either coherent or at variance with the relation (two-thirds power law) observed in active movements. In Experiment 1 participants compared the horizontal and vertical extent of the ellipses. Kinematics affected aspect ratio discrimination: The direction along which the movement decelerated was subjectively stretched. In Experiment 2 participants used the left arm to reproduce in real time the movement of the right arm. The trajectories of the left arm presented a stretch similar to the perceptual illusion demonstrated in Experiment 1. Between-arm asynchrony suggests that the motor control system cannot use kinesthetic information that is at variance with the flow of reafferences normally associated with voluntary movements. It is argued that these interactions occur at the level of a central amodal representation of the stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceptual independence of size and weight by dynamic touch.

Historically, the existence of a size-weight illusion has led to the conclusion that perceptions of size and weight are not independent. A dependence of perceived heaviness on physical volume (perceptual separability), however, is different from a dependence on perceived volume (perceptual independence). Three experiments were conducted to evaluate perceptual independence. The relations between perceived size and weight and physical size and mass were evaluated in Experiment 1. Perceived weight, length, and width were structured only by the corresponding physical variables, whereas variations in volume were not separable from variations in mass. F. G. Ashby and J. T. Townsend's (1986) test for perceptual independence was applied in Experiment 2. Perceived weight was independent of perceived length and volume. Experiment 3 used a magnitude estimation paradigm to investigate the extent to which information-perception relations could be related to the observed patterns of separability and independence. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of pictorial illusion on prehension and perception

The present study examined the effect of a size-contrast illusion (Ebbinghaus or Titchener Circles Illusion) on visual perception and the visual control of grasping movements. Seventeen right-handed participants picked up and, on other trials, estimated the size of "poker-chip" disks, which functioned as the target circles in a three-dimensional version of the illusion. In the estimation condition, subjects indicated how big they thought the target was by separating their thumb and forefinger to match the target's size. After initial viewing, no visual feedback from the hand or the target was available. Scaling of grip aperture was found to be strongly correlated with the physical size of the disks, while manual estimations of disk size were biased in the direction of the illusion. Evidently, grip aperture is calibrated to the true size of an object, even when perception of object size is distorted by a pictorial illusion, a result that is consistent with recent suggestions that visually guided prehension and visual perception are mediated by separate visual pathways.     

A motor signal and "visual" size perception

Recent models of the visual system in primates suggest that the mechanisms underlying visual perception and visuomotor control are implemented in separate functional streams in the cerebral cortex. However, a little-studied perceptual illusion demonstrates that a motor-related signal representing arm position can contribute to the visual perception of size. The illusion consists of an illusory size change in an afterimage of the hand when the hand is moved towards or away from the subject. The motor signal necessary for the illusion could be specified by feedforward and/or feedback sources (i.e. efference copy and/or proprioception/kinesthesis). We investigated the nature of this signal by measuring the illusion's magnitude when subjects moved their own arm (active condition, feedforward and feedback information available), and when arm movement was under the control of the experimenter (passive condition, feedback information available). Active and passive movements produced equivalent illusory size changes in the afterimages. However, the illusion was not obtained when an after-image of subject's hand was obtained prior to movement of the other hand from a very similar location in space. This evidence shows that proprioceptive/kinesthetic feedback was sufficient to drive the illusion and suggests that a specific three-dimensional registration of proprioceptive input and the initial afterimage is necessary for the illusion to occur.     

How Perception Impacts on Drawings.

In 3 experiments the authors investigate how errors in perception produce errors in drawings. In Experiment 1, when Shepard stimuli were shown as a pair of tables, participants made severe errors in trying to adjust 1 part of the stimulus to match the other. When the table legs were removed, revealing a pair of parallelograms with minimal perspective cues, the illusion was weaker. The authors predicted that participants would err when drawing the table but not the parallelogram stimuli. The results of Experiment 2 support the prediction and establish a direct link between degree of perceptual distortion of the table stimuli and the severity of error in drawing. When drawing only the right-hand part of the figure, participants also erred to a greater degree in drawing the table than the parallelogram (Experiment 3). Collectively, the results suggest that perceptual distortion is linked with errors in drawing the table stimuli. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Geometrical illusions can affect time-to-contact estimation and mimed prehension.

Results indicate that under some conditions the Sander parallelogram illusion can affect time-to-contact (TTC) estimation in a prediction-motion (PM) task and in an interceptive action (IA). The illusion also affected mimed manual prehension. The implication is that the timing of responses in the PM and IA tasks may involve an estimate of TTC that is based on the perceived dimensions of the environment. Further research is warranted in the development of models of perceived collision and of visually guided actions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Mood and the correction of positive versus negative stereotypes.

The present research examined the effects of sadness on the correction of social stereotypes. Participants who either were or were not induced to feel sad were asked to form an impression of a single individual who belonged to a group that had either stereotypically positive or negative implications. Experiments 1 and 2 showed that sad people corrected for their negative, but not for their positive stereotypes. Experiment 3 demonstrated that this asymmetry was not due to stereotype valence per se but to whether the stereotype was perceived as an inappropriate basis for judgment. A model is presented that suggests that sad people do not simply ignore category-based information, but rather correct for their stereotypes only when they are perceived as inappropriate, which tends to be more often the case if the stereotype is negative than if it is positive. The implications of the present results for 4 extant models of mood and information processing are discussed. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Perceptual and decisional factors influencing the discrimination of inversion in the Thatcher illusion.

The Thatcher illusion (Thompson, 1980) is considered to be a prototypical illustration of the notion that face perception is dependent on configural processes and representations. We explored this idea by examining the relative contributions of perceptual and decisional processes to the ability of observers to identify the orientation of two classes of forms—faces and churches—and a set of their component features. Observers were presented with upright and inverted images of faces and churches in which the components (eyes, mouth, windows, doors) were presented either upright or inverted. Observers first rated the subjective grotesqueness of all of the images and then performed a complete identification task in which they had to identify the orientation of the overall form and the orientation of each of the interior features. Grotesqueness ratings for both classes of image showed the standard modulation of rated grotesqueness as a function of orientation. The complete identification results revealed violations of both perceptual and decisional separability but failed to reveal any violations of within-stimulus (perceptual) independence. In addition, exploration of a simple bivariate Gaussian signal detection model of the relationship between identification performance and judged grotesqueness suggests that within-stimulus violations of perceptual independence on their own are insufficient for producing the illusion. This lack of evidence for within-stimulus configurality suggests the need for a critical reevaluation of the role of configural processing in the Thatcher illusion. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

The Doppler illusion: The influence of dynamic intensity change on perceived pitch.

Four studies illustrate a new auditory illusion associated with the Doppler effect and demonstrate a new influence of dynamic intensity change on perceived pitch. Experiment 1 confirmed the existence of a popular belief that the pitch of a moving sound source rises as the source approaches. Because there is no corresponding rise in frequency, the authors refer to the perceived pitch rise as the Doppler illusion. Experiment 2 confirmed that the effect occurs perceptually, so the belief in a "naive principle" of physics has a perceptual basis. Experiment 3 confirmed the effect does not occur under matched static conditions. Experiment 4 showed that the influence of dynamic intensity change on perceived pitch occurs outside the realm of Doppler stimuli. The findings support a dynamic dimensional interaction of pitch and loudness, with marked differences in the perception of pitch and loudness under static and dynamic conditions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of global versus local processing styles on assimilation versus contrast in social judgment.

The authors propose a global/local processing style model (GLOMO) for assimilation and contrast effects in social judgment. GLOMO is based on Schwarz and Bless' (1992, 2007) inclusion-exclusion model, which suggests that when information is included into a category, assimilation occurs, whereas when information is excluded from a category, contrast occurs. According to GLOMO, inclusion versus exclusion should be influenced by whether people process information globally or locally. In 5 experiments, using both disambiguation and social comparison, the authors induced local versus global processing through perceptual tasks and time perspective and showed that global processing produced assimilation, whereas local processing produced contrast. The experiments showed that processing styles elicited in one task can carry over to other tasks and influence social judgments. Furthermore, they found that hemisphere activation and accessibility of judgment-consistent knowledge partially mediated these effects. Implications for current and classic models of social judgment are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Absence of size congruency effects in amnesic patients' recognition: A failure of perceptually based recollection.

This study examined the status of recollection in amnesia when recollection is supported by perceptual rather than conceptual processes. Two experiments investigated the size congruency effect--the advantage in recognition of patterns presented in the same size, rather than in different sizes--at study and test. In Experiment 1, the authors used a remember-know paradigm in nonamnesic individuals and demonstrated that the size congruency effect was due to enhanced recollection. In Experiment 2, the authors examined whether amnesic patients would show a size congruency effect when their overall level of performance was matched to that of controls. Amnesic patients failed to show a size congruency effect. These findings provide evidence for a disproportionate disruption in recollection compared with familiarity in amnesia, even when recollection is supported by perceptual processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hand deviations away from visual cues: indirect evidence for inhibition

Previous research has demonstrated that when a stimulus is to be ignored, the path of motion towards a target (saccade or manual reach) deviates away from the to-be-ignored stimulus. Path deviations in saccade and reaching tasks have, however, been observed in very different situations. In the saccade tasks subjects initially attended to a cue, then disengaged attention while saccading to a target. By contrast, in the selective reaching tasks attention was continuously withdrawn from the to-be-ignored stimulus, as this was irrelevant throughout the experiment. In the two experiments reported here, cues similar to those studied in saccade tasks are examined with selective reaching procedures. Experiment 1 shows that when a coloured light-emitting diode cue, upon which subjects engage and then subsequently disengage attention, is close to the responding hand, the hand deviates away from the cue. Experiment 2 confirms this cue avoidance by showing that, compared with central fixation alone, the hand veers away from a central cue. These results confirm that the path deviations observed in saccades can also be obtained in manual reaching movements. Such findings support the notion that eye and hand movements are both affected by inhibitory mechanisms of attention.     

The effect of emergent features on judgments of quantity in configural and separable displays.

Two experiments investigated effects of emergent features on perceptual judgments of comparative magnitude in three diagrammatic representations: kiviat charts, bar graphs, and line graphs. Experiment 1 required participants to compare individual values; whereas in Experiment 2 participants had to integrate several values to produce a global comparison. In Experiment 1, emergent features of the diagrams resulted in significant distortions of magnitude judgments, each related to a common geometric illusion. Emergent features are also widely believed to underlie the general superiority of configural displays, such as kiviat charts, for tasks requiring the integration of information. Experiment 2 tested the extent of this benefit using diagrams with a wide range of values. Contrary to the results of previous studies, the configural display produced the poorest performance compared to the more separable displays. Moreover, the pattern of responses suggests that kiviat users switched from an integration strategy to a sequential one depending on the shape of the diagram. The experiments demonstrate the powerful interaction between emergent visual properties and cognition and reveal limits to the benefits of configural displays for integration tasks. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Manipulation with no or partial vision.

The present research investigated the role of vision in closed- and open-loop processing during manipulation. In Experiment 1, participants performed common manipulatory tasks with 100% accuracy in less than 1 s without vision. In Experiment 2, the effects of extensive practice of a peg-in-hole task were examined within 4 functionally significant stages of manipulation. Performance was consistently faster with than without vision in the prereach, grasp, and transport + insert stages; reverse effects were observed during the reach stage. In Experiment 3, the effects of practice with partial vision were examined: Participants initially learned the peg-in-hole task with full vision and then transferred to learning the same task with vision available only during 1 functional stage. Overall, performance was fastest when vision was limited to the prereach and reach stages. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Perceived shrinkage of motion paths.

We show that human observers strongly underestimate a linear or circular trajectory that a luminous spot follows in the dark. At slow speeds, observers are relatively accurate, but, as the speed increases, the size of the path is progressively underestimated, by up to 35%. The underestimation imposes little memory load and does not require tracking of the trajectory. Most importantly, we found that underestimation occurred only when successive motion vectors changed in direction. This suggests a perceptual rather than representational origin of the illusion, related to vector-sum integration over time of neural motion signals in different directions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrete dynamic systems: the effect of perceptual structuring on composition and transfer of knowledge about operating sequences

This paper reports two experiments in which we explored the impact of perceptual grouping of elements on the organization and use of knowledge about how to operate a device. Experiment 1 explored the effects of different perceptual display regions on the creation of chunks when sequences of inputs had to be reproduced. The effects of regions were not homogeneous, but rather their influence depended on interactions between different modalities and learning conditions. Experiment 2 investigated the influence of grouping-induced composition of knowledge elements on the transfer of sequential knowledge. Two different learning criteria were used in the acquisition phase to manipulate the degree of composition of knowledge elements. In the transfer phase, subjects could transfer (1) the whole sequence of one region, (2) two partial sequences of adjacent regions, or (3) single components. It was found that regional invariance and immediate succession of components were both important for transfer performance. These results suggests that the temporal order of regions is important for the organization and use of sequential knowledge, and not the grouping of elements by itself.     

Unitization during category learning.

Five experiments explored the question of whether new perceptual units can be developed if they are useful for a category learning task, and if so, what the constraints on this unitization process are. During category learning, participants were required to attend either a single component or a conjunction of 5 components. Consistent with unitization, the conjunctive task became much easier with practice; this improvement was not found for the single-component task or for conjunctive tasks in which the components could not be unitized. Influences of component organization (Experiment 1), component contiguity (Experiment 2), component proximity (Experiment 3), and number of components (Experiment 4) on practice effects were found. Deconvolved response times (Experiment 5) showed that prolonged practice yielded faster responses than predicted by an analytic model that integrates evidence from independently perceived components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)