Test of a response bias model of bisection

An algebraic model of bisection —a special case of Pfanzagl’s general measurement system-was tested for brightness. Nonparametric scalability, a condition derived from reflexivity, commutativity, and bisymmetry, was disconfirmed, leading to a rejection of the commutativity axiom, and necessitating the incorporation of a response bias parameter. The systematic bias in the data was substantially reduced by the introduction of the response bias parameter-interpreted as “position” bias, not hysteresis. The data are generally supportive of Pfanzagl’s bisection system, although the failure of commutativity requires the incorporation of a response bias parameter.     

Perception of interpolated position and orientation by vision and active touch

Vision and active touch lead to similar patterns of constant error for the perception of interpolated position in twodimensional and one-dimensional regions, though the errors for touch are larger than those for vision. The error patterns for the orientation of a radius of a semicircle are more complex, but can be interpreted as due to the interaction of two sets of anchors rather than the single pair available for the linear interpolation. The greater size of the touch errors is interpreted as due to a relative overestimation of larger distances by active touch or of smallerdistances by vision.     

Temporal bisection in children

Children aged 3, 5, and 8 years received training on a temporal bisection task, with standard short and long durations being presented as visual stimuli lasting 1 and 4 s or 2 and 8 s. Nonstandard comparison stimuli were spaced linearly between the standards. Psychophysical functions showed increasing proportions of "long" responses (responses appropriate to the long standard) with increasing stimulus duration, but were flatter in the younger children than in the 8-year-olds. Bisection points (the stimulus duration giving rise to 50% "long" responses) were close to the arithmetic mean of the short and long standards in most conditions. Statistical analyses and results from different theoretical models of the data all suggested that temporal sensitivity was higher in the 8-year-olds than in the younger groups, even when the possibility of random responding was controlled for.     

One, two, three, many - Subitizing in active touch

‘Subitizing’ refers to rapid and accurate judgement of small numbers of items, while response times and error rates increase rapidly for larger set-sizes. Most enumeration studies have been done in vision. Enumeration studies in touch have mostly involved ‘passive touch’, i.e. touch without active exploration. In daily life a much more common situation is that of ‘active touch’, e.g. when we count the number of coins in our pocket. To investigate numerosity judgement in active touch, we let subjects haptically explore varying numbers of spheres. Our results show that enumeration for up to 3 items is more efficient than for larger numbers of items. We also show that enumeration in this regime was not performed through estimation. Furthermore, it is shown that numerosity information was accessed directly and not through mass or volume cues. Not only do our results show that a haptic version of subitizing exists in active touch, they also suggest similar underlying enumeration mechanisms across different modalities.     

Representational pseudoneglect in line bisection

"Representational pseudoneglect" refers to a bias toward the left side of space that occurs when visual information is remembered. Recently a number of demonstrations of such representational pseudoneglect have appeared. In the present article, we report an experiment in which we adopted the classic line bisection paradigm to study representational pseudoneglect. Participants bisected horizontal lines that were shown in extrapersonal space. When the lines were visible on the screen, there was no evidence of any leftward bias. However, when lines were bisected from memory, the participants demonstrated a clear bias to the left. This is the first demonstration of a leftward bias in the bisection of remembered visually presented lines.     

Cognition in the bisection task

Bisecting a visually presented stimulus is a sensitive test for attentional and motor biases in both healthy and brain-damaged participants. There are, in addition, perceptual effects on performance and several idiosyncratic biases. Experiments that manipulated the stimulus attributes have suggested that higher-level cognitive processes can also influence bisection accuracy. These observations encourage a wider diagnostic use of the bisection procedure.     

Discriminative touch and emotional touch.

Somatic sensation comprises four main modalities, each relaying tactile, thermal, painful, or pruritic (itch) information to the central nervous system. These input channels can be further classified as subserving a sensory function of spatial and temporal localization, discrimination, and provision of essential information for controlling and guiding exploratory tactile behaviours, and an affective function that is widely recognized as providing the afferent neural input driving the subjective experience of pain, but not so widely recognized as also providing the subjective experience of affiliative or emotional somatic pleasure of touch. The discriminative properties of tactile sensation are mediated by a class of fast-conducting myelinated peripheral nerve fibres--A-beta fibres--whereas the rewarding, emotional properties of touch are hypothesized to be mediated by a class of unmyelinated peripheral nerve fibres--CT afferents (C tactile)--that have biophysical, electrophysiological, neurobiological, and anatomical properties that drive the temporally delayed emotional somatic system. CT afferents have not been found in the glabrous skin of the hand in spite of numerous electrophysiological explorations of this area. Hence, it seems reasonable to conclude that they are lacking in the glabrous skin. A full understanding of the behavioural and affective consequences of the differential innervation of CT afferents awaits a fuller understanding of their function.     

Voluntary manual exploration and vision in rod bisection

Two experiments were carried out to investigate contributions of voluntary manual exploration and vision to rod-bisection performance when the rod was placed in different spatial positions. Analysis showed both voluntary manual exploration and vision contributed to the accuracy of rod-bisection performance in healthy adults (Exp. 1: 12 men, 13 women; Exp. 2: 10 men, 11 women). Advantages of voluntary manual exploration were related to rod position and initial search direction. Results are discussed with regard to ecological approach to action and perception, two cortical systems (ventral and dorsal streams) for perception and control of actions, and the hemispheric activation hypothesis.     

The role of spatial integration in the perception of surface orientation with active touch

Vision research has shown that perception of line orientation, in the fovea area, improves with line length (Westheimer & Ley, 1997). This suggests that the visual system may use spatial integration to improve perception of orientation. In the present experiments, we investigated the role of spatial integration in the perception of surface orientation using kinesthetic and proprioceptive information from shoulder and elbow. With their left index fingers, participants actively explored virtual slanted surfaces of different lengths and orientations, and were asked to reproduce an orientation or discriminate between two orientations. Results showed that reproduction errors and discrimination thresholds improve with surface length. This suggests that the proprioceptive shoulder-elbow system may integrate redundant spatial information resulting from extended arm movements to improve orientation judgments.     

Fingertip force,surface geometry,and the perception of roughness by active touch

Ss made magnitude estimates of the perceived roughness of grooved metal plates under conditions of active touch with controlled finger force. The wider the grooves in the plate, the narrower the lands between the grooves, or the greater the finger force, the greater was the perceived roughness. Increase in finger force also slightly increased the slope of the magnitude estimation function, suggesting not only that the roughness of a uniform surface but also the contrasts in the roughness of differing parts of a patterned surface would be altered by changes in the manner of feeling the surface. An analogous effect has been reported in vision, in that increases in illumination increase the apparent contrast of a surface.     

Detection of amplitude modulation and frequency modulation in tactual gratings: a critical bandwidth for active touch

Since most natural surfaces are complex and vary in amplitude and spatial frequency, it might be interesting to consider gratings not in the spatial domain, but in the spatial-frequency domain. Detection thresholds for amplitude modulation (AM) and frequency modulation (FM) in sinusoidal gratings were measured for seven participants. Participants moved their fingers actively across the gratings. Although the two types of modulation are quite different in the spatial domain, they have many features in common in the frequency domain. In previous research (Nefs et al 2001 Perception 30 1263-1274) we measured the discrimination thresholds for amplitude and frequency for sinusoidal gratings. We hypothesised then that these thresholds could be used to predict the discriminability of other types of gratings. In the present study, we did indeed find that the FM and AM detection thresholds can be understood quite well by these discrimination thresholds. The results indicate that the tactual system contains parallel psychophysical channels that filter and integrate the power of stimuli within critical bands. With these results, we are also able to calculate the critical bandwidth for active dynamic touch. We estimated the critical bandwidth surrounding the spatial frequency of 2 cycles cm(-1) to be about 125% of that spatial frequency. This value for the critical band for spatial frequency is incompatible with previous findings for temporal frequencies in vibrotactile research. This indicates that dynamic spatial-frequency discrimination is not likely to be done by temporal frequency.     

Invariance tests for bisection and fractionation scaling

If we are to accept the power function as the psychophysical law, then estimates of the exponent of a particular form of the power law should be independent of changes in basic independent variables. In the present study, various power law hypotheses were tested for the bisection and fractionation scaling of brightness. The results indicated that for bisection, estimates of exponents were dependent on the particular interval bisected, suggesting rejection of the simple power law for bisection. For fractionation, two additional forms of the power law were tested, each form involving a threshold parameter. One was the Φ-law (involving a translation on the intensity axis), and the other was the ψ-law (involving a translation on the psychological axis). The Φ-law provided a poor fit to the data, whereas the ψ-law appeared to fit well for at least one S. Analysis for individuals showed that for all five Ss, the variance due to standards was appreciably larger for the Φ-law.     

Representational bias does not affect bisection of lines with a pictorially or semantically defined top by patients with left hemispatial neglect

Normal subjects may have both representational and visual-based components determining bias in bisection of horizontal, vertical, and radial lines. The influence of these components is less clear in patients with neglect. We asked 25 patients with right hemisphere stroke and clinical features of neglect to bisect lines oriented horizontally, vertically, and radially above and below eye level. Objects including human silhouette figures, arrowheads, and the words 'TOP' and 'BOTTOM' were placed at either end of each line. These figures were presented either upright or upside down in some orientations, and presented rightward and leftward in other orientations, to pictorially or semantically define a "top" to each line independent of the actual top of the visual field. Patients demonstrated a rightward bias on all horizontal line bisections, with similar bias and greater magnitude than normal subjects. Patients also demonstrated visual-based biases on some of the vertical, radial down, and radial up lines presented. However, patients did not demonstrate a significant representational bias with any of the visual cues presented on any of the line orientations. Patients with acute right hemisphere stroke demonstrate a rightward bias when asked to perform line bisection in the horizontal line orientation, as well as an upward bias in vertical line bisection. The lack of representational bias in patients with neglect may be due to a greater degree of visual-based neglect as compared to representational neglect, or it may be due to an absence of representational bias in patients with right hemisphere stroke.     

Failure of additivity in bisection of length

Subjects were intructed to select one rod to lie halfway in length between two given rods. These bisection instructions imply an additive model in the subjective metric. However, the data were inherently nonadditive; the length of the bisector could be an increasing or a decreasing function of the length of one given rod, depending on the length of the other given rod. A convexity analysis and a nonmetric analysis both showed that no monotone transformation could make the data additive. The bisection problem is used to contrast the axiomatic and functional approaches to measurement theory.     

EEG captures affective touch: CT-optimal touch and neural oscillations

Tactile interactions are of developmental importance to social and emotional interactions across species. In beginning to understand the affective component of tactile stimulation, research has begun to elucidate the neural mechanisms that underscore slow, affective touch. Here, we extended this emerging body of work and examined whether affective touch (C tactile [CT]-optimal speed), as compared to nonaffective touch (non-CT-optimal speed) and no touch conditions, modulated EEG oscillations. We report an attenuation in alpha and beta activity to affective and nonaffective touch relative to the no touch condition. Further, we found an attenuation in theta activity specific to the affective, as compared to the nonaffective touch and no touch conditions. Similar to theta, we also observed an attenuation of beta oscillations during the affective touch condition, although only in parietal scalp sites. Decreased activity in theta and parietal-beta ranges may reflect attentional-emotional regulatory mechanisms; however, future work is needed to provide insight into the potential neural coupling between theta and beta and their specific role in encoding slow, tactile stimulation.     

Frontal and posterior ERPs related to line bisection

The aim of this study was to investigate the dynamic nature of the cortical visuospatial attention processes during the line bisection test, which is sensitive to perceptual asymmetries. EEGs of 26 normal volunteers were recorded during the administration of a computerized line bisection test, which requires participants mark the midline of lines using a mouse. Two event-related potentials subsequent and time locked to the line presentations, namely, P300 and a positive slow wave, were obtained. Findings suggested that both potentials were related to the test performance, and the right hemisphere was more active. Analysis suggested a right parietotemporal and superior parietal locus for the P300 and right prefrontal activity for the positive slow wave. A dynamic asymmetrical activity was identified, such that after primary visual perception, spatial processing is then initiated in the right parietotemporal cortex and then proceeds to the right prefrontal cortex.     

The location and interpretation of the bisection point

In atemporal bisectiontask with humans, the observer is required to decide whether a probe duration ( t ) is more similar to the short referent (S), an R S response, or to the long referent (L), an R L response. Temporal bisection yields a psychometric function relating the proportion of long responses, P(R L ), to probe duration t . The value of t at which R S and R L occur with equal frequency, P(RL) = .5, is referred to as the bisection point, T 1/2 . Bisection models usually interpret T 1/2 as identifying the value of t that is equally confusable with S and L, but they differ in their predictions for the location of T 1/2 . The present paper presents new data relevant to the location and interpretation of T 1/2 . The data indicate that the empirical values usually are biased, the biases being influenced by duration range, L:S ratio, and probe spacing. Moreover, the biases often are not consistent across observers. It is concluded that empirical values of T 1/2 should not be interpreted as indicating the value of t that is equally confusable with S and L.