Perception

The human egocentric perception of approaching objects and the related perceptual processes have been of interest to researchers for several decades. This article gives a literature review on numerous studies that investigated the phenomenon when an object approaches an observer (or the other way around) with the goal to single out factors that influence the perceptual process. A taxonomy of metrics is followed by a breakdown of different experimental measurement methods. Thereinafter, potential factors affecting the judgment of approaching objects are compiled and debated while divided into human factors (e.g., gender, age, and driving experience), compositional factors (e.g., approaching velocity, spatial distance, and observation time), and technical factors (e.g., field of view, stereoscopy, and display contrast). Experimental findings are collated, juxtaposed, and critically discussed. With virtual-reality devices having taken a tremendous developmental leap forward in the past few years, they have been able to gain ground in experimental research. Therefore, special attention in this article is also given to the perception of approaching objects in virtual environments and put in contrast to the perception in reality.

When two eyes view dissimilar images, an observer typically reports ambiguous perception called binocular rivalry where the subjective perception fluctuates between the two inputs. This perceptual instability is often comprised of exclusive dominance of each image and a transition state called piecemeal state where the two images are intermingled in patchwork manner. Herein, we investigated the effects of multimodal association of sensory congruent pair, arbitrary pair, and reverse pair on piecemeal state in order to see how each level of association affects the ambiguous perception during binocular rivalry. To induce the multisensory associations, we designed a matching task with audiovisual feedback where subjects were required to respond according to given pairing rules. We found that explicit audiovisual associations can substantially affect the piecemeal state during binocular rivalry and that this congruency effect that reduces the amount of visual ambiguity originates primarily from explicit audiovisual association training rather than common sensory features. Furthermore, when one information is associated with multiple information, recent and preexisting associations work collectively to influence the perceptual ambiguity during rivalry. Our findings show that learned multimodal association directly affects the temporal dynamics of ambiguous perception during binocular rivalry by modulating not only the exclusive dominance but also the piecemeal state in a systematic manner.

Previous research has demonstrated that Panum’s fusional range increases in the periphery, and this increase is usually attributed to eccentricity. However, it is unclear whether the increase in the periphery is driven by eccentricity or separation between the stimulus and the central fixation marker. In Experiment 1, we independently measured the effects of eccentricity and stimulus separation on Panum’s fusional range for horizontal disparities. We observed significant increases in Panum’s range as eccentricity increased independently of stimulus separation. Experiment 2 revealed that the extent of Panum’s fusional range for vertical disparities increased with eccentricity independently of stimulus separation. Taken together, these results strongly support previously held conclusions that Panum’s fusional range for both horizontal and vertical disparities increases with increasing eccentricity and is little impacted by stimulus separation.

Recently, it has been proposed that solving addition and subtraction problems can evoke horizontal shifts of spatial attention. However, prior to this study, it remained unclear whether orienting shifts of spatial attention relied on actual arithmetic processes (i.e., the activated magnitude) or the semantic spatial association of the operator. In this study, spatial–arithmetic associations were explored through three experiments using an eye tracker, which attempted to investigate the mechanism of those associations. Experiment 1 replicated spatial–arithmetic associations in addition and subtraction problems. Experiments 2 and 3 selected zero as the operand to investigate whether these arithmetic problems could induce shifts of spatial attention. Experiment 2 indicated that addition and subtraction problems (zero as the second operand, i.e., 2 + 0) do not induce shifts of spatial attention. Experiment 3 showed that addition and subtraction arithmetic (zero as the first operand, i.e., 0 + 2) do facilitate rightward and leftward eye movement, respectively. This indicates that the operator alone does not induce horizontal eye movement. However, our findings support the idea that solving addition and subtraction problems is associated with horizontal shifts of spatial attention.

When people choose between two items, they usually look at them alternately before deciding. The frequency and duration of contact are usually determined unconsciously. However, in a previous study, looking at one item for longer than the other increased participants’ preference for the former, but only when they had to move their eyes to look at each item. This result implies that eye movements not only gather information but are also closely related to decision-making. By analogy, this study examines the relation between hand movements and haptic preference. When participants touched two handkerchiefs in a pre-determined order before choosing the one they preferred, the likelihood of choosing the more frequently touched handkerchief was greater than chance. Bias in the choice was greater with increased difference in the frequency of touching between the two handkerchiefs. It was also greater when participants moved their arm to touch the handkerchiefs, compared with when a machine carried the handkerchiefs to their hand. These results indicate that both the reaching movement for touching and the frequency of touching affect the preference judgment using haptics.

To investigate the effect of heat, moisture transfer, and mechanical tactile properties of fabrics on skin wetness perception when fabrics were in dynamic contact with skin at three velocities, nine knitted fabrics varying in fiber composition, thickness, and surface texture were evaluated by 20 participants using a wetness rating scale. The objective physical properties of the fabrics, namely, heat and moisture transfer and surface texture, and human physiological responses, namely, skin cooling rate and myoelectric signals, under various conditions were measured, and their correlations with the subjective wetness perception were studied. While the results indicated a significant influence of fabric type, water content, and velocity on skin wetness perception, no significant relation between electromyography and wetness perception was found. Fabrics with faster water spreading speeds and lower absorption rates were perceived as less wet, and the maximum transient thermal flow and skin cooling rate had a significant positive correlation with wetness perception. Furthermore, subjective wetness perception was predicted by the physical parameters of the fabric, that is, maximum transient thermal flow, water content, and friction coefficient, with an acceptable goodness of fit (R² = 0.82, p < .001).

Rubber hand illusion is caused by spatiotemporally congruent visuotactile stimulation which induces a sense of ownership towards a fake limb. We tested two predictions of the Bayesian bottom-up model; namely, that the strength of the illusion is inversely proportional to (a) the distance separating hands and (b) the precision of proprioceptive signals. To manipulate distance, we displaced participants’ hands to either a position close to (8 cm) or far from (24 cm) the rubber hand. Before manipulation, we assessed proprioceptive abilities in a task requiring active reproduction of one’s arm’s position. Proprioceptive precision was operationalised as inversely related to the variance of the estimations. Multiple regression showed that both for subjective and physiological measures neither distance, nor proprioceptive precision, nor their interaction were predictors of illusion strength. Bayes factor analyses provided evidence for null effects. Our findings suggest the limited relevance of proprioception for the strength of visuo-haptically induced rubber hand illusion.

Interlacing one’s fingers can cause misperception of finger positions. Observer’s (O’s) fingers were interlaced in six different ways and experimenter (E) tapped two adjacent fingers in quick succession (e.g., tapping the right middle finger then the left ring finger). O had to state the perceived direction in which the tapping occurred, and errors were recorded. When hands were well separated, touching two adjacent fingers of one hand gave error rates of only 2.4%, and touching a finger on one hand then the other gave error rates of only 3.4%. Interlacing the fingers as if in prayer increased error rates to 9%. When hands were superimposed with finger pointing away from O’s body, error rates rose further to 30%. Observers knew which fingers were which, but they were confused about exactly where their fingers were. Thus, somatotopic was greatly superior to spatiotopic localization.