Dissociation between visual perception of allocentric distance and visually directed walking of its extent

Walking without vision to previously viewed targets was compared with visual perception of allocentric distance in two experiments. Experimental evidence had shown that physically equal distances in a sagittal plane on the ground were perceptually underestimated as compared with those in a frontoparallel plane, even under full-cue conditions. In spite of this perceptual anisotropy of space, Loomis et al (1992 Journal of Experimental Psychology. Human Perception and Performance 18 906-921) found that subjects could match both types of distances in a blind-walking task. In experiment 1 of the present study, subjects were required to reproduce the extent of allocentric distance between two targets by either walking towards the targets, or by walking in a direction incompatible with the locations of the targets. The latter condition required subjects to derive an accurate allocentric distance from information based on the perceived locations of the two targets. The walked distance in the two conditions was almost identical whether the two targets were presented in depth (depth-presentation condition) or in the frontoparallel plane (width-presentation condition). The results of a perceptual-matching task showed that the depth distances had to be much greater than the width distances in order to be judged to be equal in length (depth compression). In experiment 2, subjects were required to reproduce the extent of allocentric distance from the viewing point by blindly walking in a direction other than toward the targets. The walked distance in the depth-presentation condition was shorter than that in the width-presentation condition. This anisotropy in motor responses, however, was mainly caused by apparent overestimation of length oriented in width, not by depth compression. In addition, the walked distances were much better scaled than those in experiment 1. These results suggest that the perceptual and motor systems share a common representation of the location of targets, whereas a dissociation in allocentric distance exists between the two systems in full-cue conditions.     

Error in visually directed manual pointing

Errors in pointing at visual targets without sight of the hand or arm were measured for both hands in two cue conditions. The existence of large errors of overreaching, which increase as cues are reduced, was confirmed. These vary with target distance but not appreciably with the hand used or the target direction. Large lateral errors were also found. These can be reasonably well described by rotations about the midpoint of the eyes. Their magnitude and direction depend on the subject and the hand used, but are largely independent of cue condition and distance. The mean angular error across subjects taken without regard to sign was 4.8 deg. The mean difference between hands was 5.2 deg. The effect of eye dominance expected under the hypothesis of Walls and Ogle was not obtained     

Idiosyncratic errors in visually directed reaching

Subjects reaching with their eyes closed to visually presented targets missed their targets by an average of 4% of arm length; significant variation in the direction and magnitude of error arose from target location and idiosyncratic sources. The errors were largely unaffected by extreme variation in the arm's starting location. These data lend support to models of sensorimotor learning that focus on associations between postures and hand locations, but do not confirm a leading example of the class, exemplified by Kuperstein's (1988) circular reaction model.     

Visually directed pointing as a function of target distance,direction, and available cues

In pointing at visual targets without sight of the hand, large errors occur. There is a tendency to overreach targets, and this tendency is much greater (about 25 em) when convergence is the only cue to distance than when there are many cues (2–11 cm). Angular errors of up to 10 deg also occur. These tend to be to the side opposite the sighting eye, when the favored hand is used. The variance of the pointing response with convergence alone is reduced by approximately half with the introduction of several spatial cues. These results are interpreted as indicating that, for a target within the reach of the arm and with convergence alone as a cue, the depth signal produced by the visual system corresponds to a greater distance than that produced when many cues are available. The results are also consistent with the hypothesis that perceived direction tends to approximate direction from the sighting eye.     

Dual-egocentre hypothesis on angular errors in visually directed pointing

We examined the hypothesis that angular errors in visually directed pointing, in which an unseen target is pointed to after its direction has been seen, are attributed to the difference between the locations of the visual and kinesthetic egocentres. Experiment 1 showed that in three of four cases, angular errors in visually directed pointing equaled those in kinesthetically directed pointing, in which a visual target was pointed to after its direction had been felt. Experiment 2 confirmed the results of experiment 1 for the targets at two different egocentric distances. Experiment 3 showed that when the kinesthetic egocentre was used as the reference of direction, angular errors in visually directed pointing equaled those in visually directed reaching, in which an unseen target is reached after its location has been seen. These results suggest that in the visually and the kinesthetically directed pointing, the egocentric directions represented in the visual space are transferred to the kinesthetic space and vice versa.     

Development of the infant's hand preference for visually directed reaching: Preliminary report of a longitudinal study

The development of hand preference in infancy was investigated longitudinally by using a visually-directed reaching task. Thirty-two infants, equally divided into groups of familial right- and left-handed boys and girls, were tested every 3 weeks from 24 to 39 weeks of age and once again at 52 weeks. Group trends for the development of hand preference were differentiated by familial handedness and sex of the infant. At all ages, test object position (to the infant's right or left) strongly influenced the hand used for reaching. Marked variability both between and within infants demonstrated an instability of early hand preference, an effect that could be appreciated fully only with a prospective longitudinal design. The results thus suggest that the development of hand preference for reaching is highly variable, discontinuous, and related to the interaction of sex and familial handedness.     

A comparison of accommodative and fusional convergence as cues to distance

The effectiveness of fusional as compared with accommodative convergence (with accommodation present in both cases) in determining perceived distance was investigated in this study. Luminous frames of two different visual angles at a nearly constant distance were viewed binocularly to provide fusional convergence and monocularly to provide accommodative convergence. Although some differences in reported size and distance of the frames occurred on the first presentations for binocular as compared to monocular observation, the most systematic differences between these two types of observation were present for the second (successive) presentations of the two frame sizes to the same Os. This is attributed to the relative size cue to distance occurring as a function of the different retinal sizes on the successive presentations. It was found that this relative size cue was more effective in modifying the perceived size and distance of the second presentations for monocular than for binocular observation. It is suggested that this reflects the greater effectiveness as a cue to distance of fusional as compared with accommodative convergence. This conclusion is of importance for studies concerned with the evaluation of convergence as a determiner of perceived distance.     

Adaptation in distance perception based on oculomotor cues

Accommodation and convergence primarily serve to adjust the eyes to the distance of the object viewed, but, once made, these oculomotor adjustments serve as cues for the object’s distance. Experiments are reported that show that the relation between oculomotor adjustments and the distances they signify can be changed by adaptation to glasses that cause alteration in the oculomotor adjustments with which objects are viewed. This changed relation manifested itself in marked alterations of size perception. Wearing, for 30 min, glasses that caused a change in accommodation and convergence corresponding to a smaller object distance and equivalent to 1.5 lens diopters caused subsequent mean size increases that ranged from 50% to 65%. Adaptation to glasses that changed oculomotor adjustments in the same amount but in the opposite direction resulted in decreases in perceived sizes that varied from 18% to 40%, dependent on the distance of the test object. These were the results of size estimates obtained before and after the adaptation period under conditions where only accommodation and convergence served as cues for distance. A newly developed test of size perception was also used, in which S adjusted the size of the projected image of an array of familiar objects on a screen until the size of the objects appeared normal. Again, such adjustments were made before and after the adaptation period, and size differences were obtained that were in the direction to be expected of adaptation and varied in amount between 12% and 33%, dependent on the distance of the screen. The reason for the different amounts of size change measured by the two kinds of tests was investigated.     

Keeping one's distance: the influence of spatial distance cues on affect and evaluation

Current conceptualizations of psychological distance (e.g., construal-level theory) refer to the degree of overlap between the self and some other person, place, or point in time. We propose a complementary view in which perceptual and motor representations of physical distance influence people's thoughts and feelings without reference to the self, extending research and theory on the effects of distance into domains where construal-level theory is silent. Across four experiments, participants were primed with either spatial closeness or spatial distance by plotting an assigned set of points on a Cartesian coordinate plane. Compared with the closeness prime, the distance prime produced greater enjoyment of media depicting embarrassment (Study 1), less emotional distress from violent media (Study 2), lower estimates of the number of calories in unhealthy food (Study 3), and weaker reports of emotional attachments to family members and hometowns (Study 4). These results support a broader conceptualization of distance-mediated effects on judgment and affect.     

The language used in describing autobiographical memories prompted by life period visually presented verbal cues,event-specific visually presented verbal cues and short musical clips of popular music

Here, we examined linguistic differences in the reports of memories produced by three cueing methods. Two groups of young adults were cued visually either by words representing events or popular cultural phenomena that took place when they were 5, 10, or 16 years of age, or by words referencing a general lifetime period word cue directing them to that period in their life. A third group heard 30-second long musical clips of songs popular during the same three time periods. In each condition, participants typed a specific event memory evoked by the cue and these typed memories were subjected to analysis by the Linguistic Inquiry and Word Count (LIWC) program. Differences in the reports produced indicated that listening to music evoked memories embodied in motor-perceptual systems more so than memories evoked by our word-cueing conditions. Additionally, relative to music cues, lifetime period word cues produced memories with reliably more uses of personal pronouns, past tense terms, and negative emotions. The findings provide evidence for the embodiment of autobiographical memories, and how those differ when the cues emphasise different aspects of the encoded events.     

The effects of visually represented cues on learning of linear function rules

The effects of visually represented weight (absence or presence of a series of five weights: 1, 2, 3, 4, and 5 g) and context cues (verbal alone, verbal plus graphic, or verbal plus pictorial) for a concrete weighing operation on the acquisition rate of three linear function rules were investigated along with a nonspecific transfer control condition in a rule learning paradigm. Multivariate analyses of variance of the time, instance, and error measures indicated that the graphic and pictorial context combined with the weight cue were more effective for the faster acquisition of the coefficient rule (a·F = S) than other conditions; that the weight and the context cues were independently effective for the faster acquisition of the coefficient rule (F + b = S); and that the observed effects diminished when transferred to the last complex linear function rule task (a·F + b = S), although training on the first two rules facilitated the acquisition of the last one as compared to the control. The findings were interpreted in terms of the notion of vividness of the image mediators the fourth-grade Ss apparently developed and utilized for the acquisition of the first two rules.     

A feel for disgust: tactile cues to pathogen presence

One function of disgust is to act as a pathogen-avoidance system preventing contact with substances harbouring disease-causing organisms. Avoiding pathogens, however, requires systems for their detection. Whereas previous research on disgust has focused on visual and olfactory detection cues, one largely overlooked modality is touch. Here we examine whether tactile cues play a role in pathogen detection and activate the disgust response. Participants briefly touched and then rated stimuli varying along dimensions predicted to correlate with pathogen presence: moisture, temperature, and consistency. Results show that participants rated wet stimuli and stimuli resembling biological consistencies as more disgusting than dry stimuli and stimuli resembling inanimate consistencies, respectively. No main effect for temperature was found. We report on predicted interactions, the relationship between disgust ratings and perceived infection risk, and individual differences. Taken together, these data suggest that touch is an important modality providing information for disgust-related processes.     

The effects of instructions to subjects on the programming of visually directed reaching movements

Numerous studies of human motor control have examined the effects of constraints on the programming and execution of visually directed limb movements. Only a few studies, however, have explored how the subject's objective in making the movement affects the coordinated sequence of eye and limb movements that unfolds as the subject points to or grasps an object in space. In the present study, the characteristics of the targets and the environment remained constant while the demands for speed and accuracy were varied across blocks of trials by changing the instructions to the subject. In other words, the constraints operating in the situation were kept constant, but the objective of the movement was systematically varied by changing the relative demands for speed and accuracy. All subjects were required to point to visual targets presented on a screen in front of them. Eye position was monitored by infrared reflection. The position of each subject's hand in three-dimensional space was reconstructed by a computer-assisted analysis of the images provided by two rotary-shutter video cameras. The speed and accuracy demands of the task were varied in blocks of trials by requiring the subjects to point to the target "as quickly as you can" (speed condition); "as accurately as you can" (accuracy condition); or both "quickly and accurately" (speed/accuracy condition). The time to initiate an eye movement to the target was found to be reduced by increasing either the speed or accuracy demands of the task although the time to initiate the hand movement was reduced only in the speed condition. While the duration of the acceleration phase of the reach remained constant in real time, the duration of the deceleration phase was increased with increased demands for accuracy. As expected, both variable and absolute errors were largest in the speed condition. The findings indicated that the programming of the limb movement and its coordination with the associated eye movements were affected by varying the objective of the task.     

The contributions of static visual cues, nonvisual cues, and optic flow in distance estimation

By systematically varying cue availability in the stimulus and response phases of a series of same-modality and cross-modality distance matching tasks, we examined the contributions of static visual information, idiothetic information, and optic flow information. The experiment was conducted in a large-scale, open, outdoor environment. Subjects were presented with information about a distance and were then required to turn 180 before producing a distance estimate. Distance encoding and responding occurred via: (i) visually perceived target distance, or (ii) traversed distance through either blindfolded locomotion or during sighted locomotion. The results demonstrated that subjects performed with similar accuracy across all conditions. In conditions in which the stimulus and the response were delivered in the same mode, when visual information was absent, constant error was minimal; whereas, when visual information was present, overestimation was observed. In conditions in which the stimulus and response modes differed, a consistent error pattern was observed. By systematically comparing complementary conditions, we found that the availability of visual information during locomotion (particularly optic flow) led to an 'under-perception' of movement relative to conditions in which visual information was absent during locomotion.     

Binocular cues in the perception of distance of a point source of light

The ability to make egocentric distance estimates of a single point source of light, seen in darkness and without the cues of changing size and luminance, was investigated in sixteen observers. The attenuation required to maintain constant luminance, when the target was viewed from different distances, was shown to follow the inverse square law providing the angle subtended by the light was less than 20 s arc. Distance changes were also simulated by means of a split mirror which produced vergence cues, or by test lenses to provide accommodation cues. Over the range 0.5 to 9.2 m distance estimates were surprisingly accurate, although there was some overestimation of near and underestimation of far distances. Most observers made good judgements when only convergence cues were varied, whereas no observers made consistently good judgements when only accommodation cues were varied. The difficulties are discussed in terms of the accommodation-convergence link. When distance was simulated by changing convergence and accommodation cues, estimates were not as good as when real distance was changed. Since good estimates were made with brief target exposures, these judgements were not based on subsequent convergence or accommodation changes. It is suggested that the metric or reference against which the apparently absolute judgements were made was the efferent demand signal associated with a 'resting' position of convergence in darkness.     

Absolute and relative cues for the auditory perception of egocentric distance

Three experiments were performed to examine the reverberation cue to egocentric auditory distance and to determine the extent to which such a cue could provide 'absolute', as contrasted with 'relative', information about distance. In experiment 1 independent groups of blindfolded observers (200 altogether) were presented with broadband noise from a speaker at one of five different distances (0.55 to 8 m) in a normal hard-walled room. Half of each group of observers were presented with the sound at 0 deg azimuth, followed (after a delay) by the identical sound at 90 deg azimuth. The order of presentation was reversed for the remaining observers. Perceived distance varied significantly as a function of the physical distance to the speaker, even for the first presentations. The change in the binaural information between the 0 deg and 90 deg presentations did not significantly modify the results. For both orientations, near distances were overestimated and far distances were underestimated. Experiment 2 and 3 were designed to evaluate how much prior auditory exposure to the laboratory environment was necessary. A 200 Hz square-wave signal was presented from one of three distances (1, 2, or 6 m) to observers who had either minimal room information or an exposure which included talking within the room. Perceived distance varied significantly with physical distance regardless to exposure condition.     

An indirect measure of perceived distance from oculomotor cues

The sensitivity of an indirect method of measuring perceived distance was compared in two experiments with the direct procedure of eliciting verbal reports of distance. Perceived distance was varied by varying the oculomotor cues to object distance. The indirect method, called the “adjustable pivot method,” uses an apparatus that physically moves the stimulus object laterally concomitantly with the lateral motion of the head. The magnitude and direction of this concomitant motion determines the distance of the point around which the direction of gaze to the object rotates (the pivot distance) as the head is moved. The pivot distance at which the object appears stationary with head movement measures the apparent distance of the object. Both types of measures were found to vary systematically with the oculomotor distance of the object for points of light (Experiment 1) and extended objects (Experiment 2). A previous study has shown that the adjustable pivot method avoids cognitive errors that can distort verbal reports of distance. The present study, by demonstrating the discriminative capability of this method under conditions in which differences in perceived distance were expected to occur, provides clear evidence that the adjustable pivot method is a sensitive and useful procedure for measuring perceived distance.