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PubMed1991

On the fundamental nature of perception.

The process of recognition or isolation of one or several entities from among many possible entities is termed intellego perception. It is shown that not only are many of our everyday percepts of this type, but perception of microscopic events using the methods of quantum mechanics are also intellego in nature. Information theory seems to be a natural language in which to express perceptual activity of this type. It is argued that the biological organism quantifies its sensations using an information theoretical measure. This, in turn, sets the stage for a mathematical theory of sensory perception.

Humans↗
PubMed1993

Do component motions recombine into a moving plaid percept?

Two superimposed gratings, which differ in orientation and move independently, combine into a coherently moving plaid if the component gratings are similar. The effect on the plaid motion percept of the addition of texture to each grating was investigated. The texture disambiguates the motion of each component grating. Under the assumption of recombination of first-stage motion detectors into a second stage, which becomes available to perception, one would expect the perceived motion direction of the plaid to change as a result of texture addition. Subjects perceived the oblique motion direction of textured bars of a single orientation correctly. This occurred for texture details with dimensions down to the resolution limit in the fovea (1 min of arc). Two bar patterns with fine texture (1 min of arc details) which differ in orientation were perceived to cohere into a plaid. The plaid's motion direction, however, was independent of the parallel motion components of the bars. For coarser textures (2 and 4 min of arc details) the bar patterns were perceived to slide past one another. In addition, we found that the plaid motion percept occurred less frequently for longer motion sequences, wider bars and for a combination of the component textures at the intersections which is compatible with partial transparency of the bars. These results do not support the two-stage model of Adelson and Movshon (1982), where only the motion component perpendicular to each grating orientation is encoded and where the perception of the plaid motion results from "recombination" of these perpendicular motion components. The data are more in line with a model where first-stage motion detectors are orientation selective but without the restriction that their preferred direction of motion is perpendicular to their preferred orientation. In the second stage it is proposed that combination occurs across the orientation dimension only. This preserves the direction of motion "labels" at the output of the second stage and allows for representation of transparent as well as coherent plaid motion at this stage of processing.

Humans↗
PubMed1995

Perception of arm orientation in three-dimensional space.

The purpose of this investigation was to determine the preferred coordinate system for perception of arm (humerus) orientation in three-dimensional space. Perception of arm orientation relative to trunk-fixed versus earth-fixed axes were compared in seven human subjects. The experimenter first moved the subject's trunk and arm into a target configuration (in which the arm's orientation relative to the trunk and/or earth was perceived and memorized by the subject) and then moved the trunk and arm to a new configuration. The blindfolded subject then attempted to reproduce the target orientation of their arm relative to either the trunk (i.e., reproduce shoulder angles--intrinsic kinesthetic coordinate system) or earth-fixed axes (extrinsic kinesthetic coordinate system). Perceptual errors were similar for both shoulder (arm relative to trunk) and extrinsic (arm relative to earth) angles. However, elevation angles were perceived with greater accuracy than yaw angles in the two coordinate systems. Also, perceptual errors for arm yaw angles in the extrinsic kinesthetic coordinate system task were better predicted from changes in trunk orientation than the errors for other angles. Furthermore, four subjects matched arm yaw angle relative to the trunk-fixed axis more accurately than to the earth-fixed axis in the extrinsic coordinate system task. These results suggests a bias toward perception of yaw angles relative to trunk-fixed axes (i.e., in an intrinsic coordinate system). These data suggest that the preferred coordinate system for kinesthetic perception of arm orientation is probably fixed in the trunk.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1990

Measurement precision of a portable instrument to assess vibrotactile perception threshold.

The objective of the present study was to evaluate the reliability of a modified version of the commercially available Biothesiometer, and to examine vibrotactile perception thresholds with respect to age and gender. A standardized protocol for measuring vibrotactile perception threshold was administered to 80 subjects, once a week over 4 weeks. Inter-session variability was stable (analysis of variance for repeated measures; P greater than 0.05) and correlations were high (Pearson's: 0.87 less than or equal to r less than or equal to 0.90; P less than or equal to 0.001). For sites on both hands and feet, there was a significant increase with age (0.19 less than or equal to r2 less than or equal to 0.52; P less than or equal to 0.001). Five factor analysis of variance model showed that vibrotactile perception threshold was significantly different with stimulus site, age category and gender; no differences were observed with alcohol consumption or smoking status. The findings indicate that the measurements from this device are highly reproducible and sensitive to expected threshold differences with age and gender. The authors attribute this to technical improvements of the original apparatus, rigid adherence to test protocol and maintenance of standard conditions. This type of instrument would be useful in assessing vibrotactile perception loss in occupational health studies.

Adult↗
PubMed1984

Comparison of five methods for measurement of vibratory perception.

Five methods for the measurement of vibratory perception (using three different vibrameters ) have been compared by determining the vibratory perception threshold in 12 subjects on two days (with a 3-d interval). One device with a vibrating rod (manufactured by MUAB ) was used, the rod being applied either to the finger-tip (rod-tip) and on the proximal phalanx (rod-phalanx). The other devices were fitted with vibrating pins. In one apparatus all pins vibrated in phase (pin-phase), in the other ( Optacon ) the pins in adjacent rows vibrated in opposite phase. The latter one was used with a continuous (pin-cont) and with a "yes-no" procedure (pin-y/n). Mean vibratory perception threshold differed considerably: from 0.09 micron (pin-y/n) to 0.61 micron (pin-phase). No learning effect was found between the two days of measurement. The correlation between the measurements on both days (a measure for the reproducibility) was about the same for all methods (from 0.71 to 0.86). Intra-individual variation amounted to 30 to 50%. The low correlation of pin-cont and pin-y/n with the other methods (0.06 to 0.44), if compared with the correlations among the remaining methods (0.53 up to 0.83), suggests that with the Optacon different sensory properties are measured. Apart from the unclear relevance of the measurement of vibratory perception for early diagnosis of neurologic diseases, these results indicate that further investigation and standardization of methods is necessary before they can be used in practice as a screening-method.

Adult↗
PubMed1995

Microgenesis of the length perception of paired lines.

The changes in perception associated with exposure time are probably continuous in the microgenetic process, as is demonstrated by such phenomena as intensity change in illusions, adaptation and normalization, practice effect, aftereffects, etc. The simultaneous contrast and assimilation in the perception of length of paired lines were measured by controlling the exposure duration or repetition. In the tachistoscopic experiment, the greatest contrast appeared at an early stage of microgenesis. In the repeated presentation experiment, the perception changed from contrast to assimilation on the expanded stage of microgenesis. These changes in perception are assumed to be the results of the differentiation of set that progresses in the microgenetic process. In the fixed-set experiment, the differentiation of set was reflected in the intensity of the aftereffect. The changes in the aftereffect and the transformation into the assimilation coincided with each other when the exposure time was varied. An expansion of the conception of perceptual microgenesis to a wider range of perceptual variability is accordingly proposed.

Contrast Sensitivity↗
PubMed1990

Stratification in perception and action.

This paper discusses the concept of stratification, in the sense of levels of analysis and levels of control, in relation to human perception and performance. It is contended that functional analysis is the proper level of analysis for the domain of perception and action. This is illustrated by means of models of cognitive energetics and motor control. The functional level of analysis can be situated in between the level of symbolic representations and the level of neurophysiological mechanisms. It is also argued that the concept of levels of control provides a way of integrating or relating ecological and information-processing approaches to psychology, in the sense that ecological psychology is concerned with lower and more peripheral levels of control (coordinative structures). Finally, some remarks are made on the relation between cognition and perception and action, drawing on Piaget, and it is proposed that the concept of schema is more appropriate for the domain of perception and action than is the notion of symbolic representations.

Attention↗
PubMed1993

The visual system and levels of perception: properties of neuromental organization.

To see whether the mental and the neural have common attributes that could resolve some of the traditional dichotomies, we review neuroscientific data on the visual system. The results show that neuronal and perceptual function share a parallel and hierarchical architecture which is manifest not only in the anatomy and physiology of the visual system, but also in normal perception and in the deficits caused by lesions in different parts of the system. Based on the description of parallel hierarchical levels of active information processing in the visual brain, we suggest a concept of dissociable levels of perception, advocating that the phenomenal perception and recognition is realized in the functional integrity of a network of reciprocal cortico-cortical connections. The properties shared by neuronal and perceptional functions provide a basis for a neuromental monism in which both functions are attributed a causal role.

Cerebral Cortex↗
PubMed2000

Midazolam attenuates ketamine-induced abnormal perception and thought process but not mood changes.

PURPOSE: To determine the effects of midazolam, 30 ngxmL(-1), on altered perception, mood, and cognition induced by ketamine. METHODS: After ketamine was administered to achieve target concentrations of 50, 100, or 150 ngxmL in 11 volunteers, perception, mood, and thought process were assessed by a visual analog scale. Mini-Mental State examination (MMSE) assessed cognition. Boluses of midazolam, 30, 14.5, and 12 microgxkg(-1), were injected every 30 min to maintain the plasma concentration at 30 ngxmL(-1), which was reached 30 min after each injection. RESULTS: Ketamine produced changes in perception about the body (P < 0.01, 0.001, and 0.0001 at 30, 60, and 90 min), surroundings (P < 0.01 and 0.0001 at 60 and 90 min), time (P < 0.002 and 0.0001 at 60 and 90 min), reality (P < 0.001 and 0.0001 at 60 and 90 min), sounds (P < 0.002 at 90 min), and meaning (P < 0.05 at 90 min). Subjects felt less energetic and clearheaded (P < 0.02 and 0.05) during ketamine, midazolam, and their co-administration. Ketamine impaired thought process (P < 0.003 and 0.0001 at 60 and 90 min). Ketamine and midazolam decreased mean total MMSE and recall scores (P < 0.001 for both). Co-administration reduced the number of subjects with perceptual (body, P < 0.01 and 0.001 at 30 and 60 min) and thought process abnormalities. Within the range of observation, co-administration did not affect the changes in mood or recall. CONCLUSION: Midazolam attenuates ketamine-induced changes in perception and thought process.

Adult↗
PubMed2003

Ethnic differences in weight loss behavior among secondary school students in Beirut: the role of weight perception.

OBJECTIVES: Assessing the prevalence of weight loss attempts in Beirut, Lebanon, a country characterized by a diversity of ethnic and religious groups and examining the interplay between ethnicity, body mass index (BMI) and weight perception and their relationship to weight loss behavior. METHODS: A school-based survey of risk behaviors conducted among secondary students (grade 10-12) in 1997. Subjects consisted of 827 boys and girls, aged 15 to 23 years, the majority of whom were Moslems (65.4%). Multiple logistic regression was used to estimate the association between ethnicity and weight perception with the likelihood of trying to lose weight controlling for BMI and a number of potential covariates. RESULTS: The prevalence of weight loss attempts was 19.1% and 42.6% in boys and girls respectively. Christians were more likely to perceive themselves as overweight and to attempt weight loss than Moslems across all BMI levels, however this trend was significant in the underweight category. While controlling for BMI did not change appreciably the results observed, after controlling for weight perception, ethnic differences in weight-loss behavior disappeared. CONCLUSION: Findings of the study suggest that whereas actual weight may constitute only partially the driving force for differentials by ethnicity, the perception of body weight acts as a mediating factor in the relationship between ethnicity and weight loss behavior. Understanding the disparities in weight management behavior across various adolescent groups is key to develop culturally appropriate educational and intervention programs for the youths.

Adolescent↗
PubMed2002

Audiotactile interactions in roughness perception.

The sounds produced when we touch textured surfaces frequently provide information regarding the structure of those surfaces. It has recently been demonstrated that the perception of the texture of the hands can be modified simply by manipulating the frequency content of such touch-related sounds. We investigated whether similar auditory manipulations change people's perception of the roughness of abrasive surfaces (experiment 1). Participants were required to make speeded, forced-choice discrimination responses regarding the roughness of a series of abrasive samples which they touched briefly. Analysis of discrimination errors verified that tactile roughness perception was modulated by the frequency content of the auditory feedback. Specifically, attenuating high frequencies led to a bias towards an increased perception of tactile smoothness. In experiment 2, we replicated the rubbing-hands manipulation of previous experimenters while participants rated either the perceived roughness or wetness of their hands. The wetness scale data replicated the results in the literature, while the roughness scale data replicated the result from experiment 1. A final experiment showed that delaying the auditory feedback from the hand-rubbing reduced the magnitude of this parchment-skin illusion. These experiments demonstrate the dramatic effect that auditory frequency manipulations can have on the perceived tactile roughness and moistness of surfaces, and are consistent with the proposal that different auditory perceptual dimensions may have varying salience for different surfaces.

Adult↗
PubMed2003

Unconscious perception of non-threatening facial emotion in parietal extinction.

The success of humans as social animals relies heavily on our ability to perceive the emotional expressions conveyed by others' faces. Functional brain imaging has shown that expressions of fear and anger selectively activate the amygdala, even when the faces conveying the emotion are presented briefly and masked to prevent conscious perception (Morris et al. 1998; Whalen et al. 1998). Such results suggest that facial emotions signalling potential threat can be extracted rapidly and automatically by the human visual system, in the absence of conscious face perception. Here we asked whether a patient with spatial extinction, a profound disorder of perception due to right parietal lobe damage, would be sensitive to non-threatening (happy and sad) emotional expressions of faces that are not consciously perceived. We show that the emotion conveyed by an extinguished face in the contralesional hemifield can influence judgements of the emotion of a subsequent target face presented foveally. The finding of significant affective priming from extinguished faces fits with the proposal that facial emotion can be processed in the absence of conscious perception, and that preserved limbic and inferotemporal structures retain privileged access to the emotional content of 'unseen' faces.

Analysis of Variance↗
PubMed2005

Contribution of tactile feedback from the hand to the perception of force.

A force-matching task was used to study the influence of constraining tactile information from the hand on the perception of forces generated with the index finger flexors, the palmar prehensile grasp and with the elbow flexors. Subjects generated the same reference forces (2-10 N) with each muscle group and matched these using the corresponding muscle group in the other arm. Force perception was studied under normal conditions and when the tactile feedback from the fingertips was constrained through the use of rigid finger splints. There was no difference between the three muscle groups when matching forces under normal conditions, but when spatial tactile information from the fingertips was attenuated forces were underestimated in perceived magnitude as compared to control conditions. These results suggest that the perception of force is influenced by tactile cues that convey information about the contact surface and that distributed spatial force cues are normally used in the perception of forces generated by the hand.

Adult↗
PubMed2005

Perceptual coupling in rhythmic movement coordination: stable perception leads to stable action.

Rhythmic movement coordination exhibits characteristic patterns of stability, specifically that movements at 0 degrees mean relative phase are maximally stable, 180 degrees is stable but less so than 0 degrees, and other coordinations are unstable without training. Recent research has demonstrated a role for perception in creating this pattern; perceptual variability judgments covary with movement variability results. This suggests that the movement results could be due in part to differential perceptual resolution of the target movement coordinations. The current study used a paradigm that enabled simultaneous access to both perception (between-trial) and movement (within-trial) stability measures. A visually specified 0 degrees target mean relative phase enabled participants to produce stable movements when the movements were at a non-0 degrees relationship to the target being tracked. Strong relationships were found between within-trial stability (the traditional movement measure) and between-trial stability (the traditional perceptual judgment measure), suggestive of a role for perception in producing coordination stability phenomena. The stabilization was incomplete, however, indicating that visual perception was not the sole determinant of movement stability. Rhythmic movement coordination is intrinsically a perception/action system.

Adolescent↗
PubMed2006

On the similarities between the perception and production of elliptical trajectories.

In an earlier study, Viviani and Stucchi (J Exp Psychol Hum Percept Perform 18:603-623, 1992) have introduced a visual illusion, whereby it was shown that when subjects are asked to determine what movement of a light spot, when tracing an elliptical trajectory, appears to be most uniform, they tend to choose movements that are close to obeying the 2/3 power law (Lacquaniti et al. Acta Psychol 54:115-130, 1983) rather than constant speed movements, even though the actual changes in velocity could exceed 200%. Here we have extended the study of this illusion by directly testing the effect of the shape (eccentricity) and size (perimeter) of the elliptical trajectory, the duration of the tracing of the ellipse and the effect of fixation on the subjects' decision regarding movement uniformity. We found that the ellipse's eccentricity and tracing out speed of the elliptical trajectory significantly affect the subjects' decisions, although the effect of eccentricity seems to be stronger than that of speed. Our findings also indicated that fixation significantly affects the subject's decision for ellipses that are more eccentric. Surprisingly, the ellipse's perimeter had a much smaller effect on the subjects' decisions, although changes in the ellipse's perimeter should have the same effect on the average velocity as changes in the time it takes to trace out the ellipse. This suggested the possibility that the subjects based their decision regarding movement uniformity on other velocity variables in addition to tangential velocity. Computer simulations we have performed have led us to conclude that the subjects' perception of movement uniformity may also be based on assessing the variations in angular velocity and possibly also in affine velocity. Our behavioral and simulation studies thus suggest that the motion perception system is quite responsive to variations in the velocity along an elliptical trajectory but in a way that depends on the path's curvature. Furthermore, the movement is judged to be more uniform when there are minimal differences in angular, tangential and perhaps also in affine velocities, along the trajectory. Our results suggest the existence of similar underlying constraints that affect both the motion perception and production systems when the movements are associated with very large velocities or large changes in velocity along more curved portions of the trajectory. Our observations therefore provide further insight into the possibility that these constraints are either imposed by the underlying neuronal dynamics, the internal architecture of the cortical neural populations or the variables used in the coding of both sensory and motor information regarding movement.

Adolescent↗
PubMed2006

Perception of angular displacement without landmarks: evidence for Bayesian fusion of vestibular, optokinetic, podokinesthetic, and cognitive information.

The perception of angular displacement during self turning is generally based on a combination of redundant signals from different sources. For example, during active turning in a visually structured environment devoid of landmarks, podokinesthetic, vestibular, and optokinetic velocity signals are fused and integrated over time to yield a unitary percept of the ongoing change in angular position ('podokinesthetic' refers to proprioceptive and corollary signals related to leg and foot movement). Previously we have shown that the fusion of two of these afferents improves perceptual accuracy and reliability in comparison to when only one is available. For example, with only a single modality available, slow rotations are perceived to be significantly larger than fast ones, whereas the combination of two modalities greatly reduces this difference. These observations spurred the hypothesis that displacement perception results from a weighted average of bottom-up (sensory) signals and top-down signals (a priori knowledge or expectation), with the weight of the latter decreasing the more sensory information is available. We now ask (1) whether the accuracy of angular displacement estimation can be further improved if it can draw on all three sensory modalities instead of only two, and (2) whether bottom-up sensory and top-down a priori information is combined for displacement estimation in a statistically optimal way. To this end 12 healthy subjects (Ss) standing on a turning platform surrounded by a rotatable optokinetic pattern were exposed to 6 different sensory conditions: pure podokinesthetic (P), vestibular (V), or optokinetic (O) stimulation, and combined podokinesthetic-vestibular (PV), vestibular-optokinetic (VO), or podokinesthetic-vestibular-optokinetic (PVO) stimulation. Stimuli had constant angular velocities of either 15, 30, or 60 degrees /s. Subjects were to press a signal button when they felt that angular displacement had reached a previously instructed magnitude (150-900 degrees ). In agreement with earlier observations, the combination of two sensory signals improved the accuracy of displacement perception by reducing both the variance of subjects' displacement estimates and their dependence on turning velocity. Adding a third sensory signal (condition PVO) led to a further reduction of variance and almost eliminated the effect of velocity. We show that these experimental results are compatible with a probabilistic fusion mechanism based on Bayes' law. This mechanism would operate on logarithmic representations of turning velocity and proceed in two stages. A first stage fuses all available bottom-up information to create a unitary representation of the velocity signalled by the different sensory modalities. A second stage then fuses this sensory information with top-down a priori information; the latter creates a bias in favour of a 'default velocity' that grows as the uncertainty of the sensory information increases. Our experimental data agree with the relation between (1) the variance of displacement estimates and (2) their modulation by velocity predicted by this scheme.

Adolescent↗
PubMed2006

Depth perception in cerebellar and basal ganglia disease.

There is increasing evidence that the cerebellum and the basal ganglia serve not only a role in motor control but also in visual perception. Patients with Parkinson's disease (PD) as well as patients with cerebellar lesions exhibit impairments of vision that are not fully explained by ocular motor deficits. It is less clear to which extent these visual deficits contribute to an impaired control of visually guided movements. This study examined whether a dysfunction of the cerebellum or the basal ganglia induces impairments in depth perception, which affect action. We employed an illusionary display, the Ames trapezoidal window, to determine the ability of PD patients (n=10) and patients with spinocerebellar ataxia (SCA) (n=6) to process depth cues when estimating object slant. Participants either pointed to the edges of the window (motor judgement) or verbally indicated the perceived orientation of the display (verbal judgement). To control for ocular and limb motor deficits, participants judged the slant of a non-illusionary display in a second task. Slant estimation of the non-illusionary window was not impaired in either patient group when compared to control subjects (all P>0.2). In contrast, SCA as well as PD patients exhibited significantly greater slant estimation errors than controls when pointing to the illusionary window (P=0.005). In addition, both patient groups made larger errors than controls in their verbal judgements during binocular viewing of the illusion (P=0.005), but not during monocular viewing (P>0.2). In sum, the present findings point towards a role for both the basal ganglia and cerebellum for the processing of visual information about depth. Since the deficits were seen both in the context of action and perception and were only partially reconciled by the availability of binocular depth cues, we conclude that basal ganglia as well as cerebellar disease may affect the visual perception of depth.

Adult↗
PubMed1999

Are perception and action affected differently by the Titchener circles illusion?

In the present study, we investigated the effects of the Titchener circles illusion in perception and action. In this illusion, two identical discs can be perceived as being different in size when one is surrounded by an annulus of smaller circles and the other is surrounded by an annulus of larger circles. This classic size-contrast illusion, known as Ebbinghaus or Titchener Circles Illusion, has a strong perceptual effect. By contrast, it has recently been demonstrated that when subjects are required to pick up one of the discs, their grip aperture during reaching is largely appropriate to the size of the target. This result has been considered as evidence of a clear dissociation between visual perception and visuomotor behaviour in the intact human brain. In this study, we suggest and investigate an alternative explanation for these results. We argue that, in a previous study, while perception was subjected to the simultaneous influence of the large and small circles displays, in the grasping task only the annulus of circles surrounding the target object was influential. We tested this hypothesis by requiring 18 subjects to perceptually estimate and grasp a disc centred in a single annulus of Titchener circles. The results showed that both the perceptual estimation and the hand shaping while grasping the disc were similarly influenced by the illusion. Moreover, the stronger the perceptual illusion, the greater the effect on the grip scaling. We discuss the results as evidence of an interaction between the functional pathways for perception and action in the intact human brain.

Adult↗