Transfer of the curvature aftereffect in dynamic touch.

TL;DR: The existence and intermanual transfer of curvature aftereffects for dynamic touch were investigated and it is concluded that the representation of object information depends on the exploration mode that is used to acquire information.

About: This article is published in Neuropsychologia.The article was published on 2008-10-01 and is currently open access. It has received 21 citations till now. The article focuses on the topics: Curvature.

Summary

1. Introduction

• A haptic curvature aftereffect is a phenomenon in which a flat surface feels concave after the prolonged touching of a convex surface, and vice versa.
• Later, they showed that the aftereffect also occurred when small variations in the exploration manner were applied, but no aftereffect was found when the adaptation and test stimuli were touched by different hands (Vogels, Kappers, & Koenderink, 1997).
• Existence of an aftereffect when curved surfaces were statically touched by only a single fingertip (Van der Horst et al., 2008).

1.1. Exploration modes to perceive curvature

• The haptic perception and representation of curvature has been investigated for several manners of exploration.
• This exploration manner is appropriate to obtain information from highly curved surfaces.
• Psychophysical studies have shown that this exploration manner is opsych B.J. van der Horst et al. /.
• Nevertheless, the shape of weakly curved stimuli can be perceived by static touch when the contact length with the stimulus is increased by placing the whole finger or several fingers together on the stimulus surface (Pont, Kappers, & Koenderink, 1997; Pont et al., 1999).
• The thresholds decreased with increasing contact length, up to about 0.5 m−1 for a contact length of 15 cm.

1.2. Representation of curvature information

• Static and dynamic touch provide different ways to acquire shape information from an object.
• This suggests that curvature information is processed in a different way for dynamic touch.
• The representation level of the curvature information may depend on the exploration mode.
• More insight into the representation of curvature information can be obtained by studying the aftereffect and its transfer.
• In vision, establishing aftereffect transfer has successfully uncovered the representation of perceived phenomena like motion (see e.g., Mather, Verstraten, & Anstis, 1998; Moulden, 1980; Tao, Lankheet, van de Grind, & van de Wezel, 2003; Wade, Swanston, & de Weert, 1993).

1.3. Active and passive dynamic touch

• A distinction is made between active and passive dynamic touch.
• In active dynamic touch, the subject moves the finger over the surface of a fixed stimulus; in passive dynamic touch, the stimulus moves underneath a finger that the subject keeps at a fixed position.
• Passive dynamic touch shares with active dynamic touch that there is an analogous moving contact between the finger and the stimulus.
• Therefore, similar results might be expected for active and passive dynamic touch.
• Passive dynamic touch has in common with static touch that the finger stays in the same location.

2. Experiment 1

• In the first experiment, the authors studied the existence and transfer of a dynamic aftereffect in active and passive dynamic touch.
• The first goal was to demonstrate the existence of a curvature aftereffect in dynamic touch.
• Having the same ability to acquire shape information does not necessarily imply that this information is represented at the same level.
• Thus, the transfer pattern might deviate from the transfer characteristics of static aftereffects, as previously reported (Van der Horst et al., 2008; Vogels et al., 1997).
• The shape could not be deduced from the immediate contact between the finger and the stimulus, but movement was required.

2.1.1. Design

• Four conditions were studied in a two × two design.
• The exploration mode was either active or passive dynamic touch.
• In the active mode, the stimuli were explored by a self-induced movement with the index finger over the surface of a stationary stimulus.
• A further distinction was made between the employment of either a single finger or different fingers.
• In the same-finger mode, the same index finger was used to touch both the adaptation and the test stimulus; in the oppositefinger mode, the right index finger touched the adaptation stimulus, and the left index finger touched the test stimulus.

2.1.2. Setup

• Subjects were seated behind a table, with their arms resting on a support.
• Only the right slit was used in the same-finger mode.
• The platform remained in position in the active conditions.
• Fig. 1 illustrates the setup of the experiment.

2.1.4. Procedure

• During a trial, the adaptation stimulus was touched by the index finger of the right hand for 11 s.
• Three back-and-forth movements were made during the adaptation phase.
• After 4 s, the test stimulus was touched with an index finger for a single side-to-side movement.
• Practice trials were conducted to accustom the subjects to the proper exploration time.
• The order in which the experimental conditions were conducted was partly counterbalanced.

2.1.5. Subjects

• Eight, paid subjects participated (four male and four female, mean age 21 years).
• All subjects were right-handed, as established by a standard questionnaire (Coren, 1993).

2.1.6. Analysis

• For each subject and condition, the responses in the convex adaptation trials were separated from the responses in the concave adaptation trials.
• A psychometric function (cumulative Gaussian) was fitted to the data to determine the point of subjective equality (PSE).
• In the active conditions, the adaptation and test stimuli were stimuli moved underneath the index finger.
• The dark bars represent the results for nger.
• The PSEs and the magnitude of the aftereffect are indicated.

2.2. Results

• The mean results for each condition are given in Fig. 3a.
• The error bars represent the standard errors.
• Visual inspection of this graph shows that an aftereffect was obtained in all conditions.
• In addition, the magnitude of the aftereffect was higher in the active conditions compared to the passive conditions.

2.3. Discussion

• This experiment shows the existence of a dynamic curvature aftereffect and, most surprisingly, a full transfer of this effect.
• This result differs from the partial transfer of the static curvature aftereffect, as obtained in their previous study (Van der Horst et al., 2008).
• To place the finding in a broader perspective, only some specific visual motion aftereffects show a full interocular transfer.
• In general, there is only partial transfer of the effect, the strength of which depends on several stimulus and measurement parameters (Tao et al., 2003; Wade et al., 1993).
• Furthermore, the difference in magnitude of the aftereffect indicates that there are differences in curvature representation of active and passive dynamic touch.

3. Experiment 2

• In the second experiment, the transfer between active and passive dynamic touch was investigated.
• In the passive–active condition, the order was reversed.
• In both conditions, subjects used only their right hands for adaptation and testing.
• Before the experiment, the authors formulated two main hypotheses.
• Second, a higher aftereffect could be obtained in the active–passive condition; this would suggest that active and passive touch share the same representation, but adaptation is stronger for active touch.

3.1. Methods

• The same setup was used for this experiment as in the previous experiment.
• The authors did not use the ±1.8 m−1 stimuli but increased the number of repetitions per stimulus.
• The order in which the experiment was performed was counterbalanced among subjects.
• There were eight, right-handed subjects (four male and four female, mean age 21 years), none of whom were involved in the first experiment.

3.2. Results

• The mean results for each condition are presented in Fig. 3b.
• Independent samples t-tests were performed in order to compare the results of the second experiment to the same-finger results of the first experiment.
• The result for the passive–active condition was not significantly different from that of the active condition but was significantly higher than that of the passive condition (t14 = 0.7, p = 0.5 and t14 = 3.9, p = 0.001, respectively).

3.3. Discussion

• This experiment reveals an aftereffect transfer from active to passive dynamic touch, and vice versa.
• The magnitude of the effect was higher in the passive–active condition than in the active–passive condition.
• The correspondence between the first and the second experiment is that a stronger aftereffect is obtained when the test stimulus is actively explored, irrespective of the manner of touching the adaptation stimulus.

4.1. The existence of a dynamic curvature aftereffect

• The authors demonstrated the occurrence of an aftereffect when curved surfaces are dynamically touched with a single index finger.
• This finding is a considerable extension of the original discovery of Gibson (1933), since the authors employed a quantitative approach and displayed the existence of the effect for a relatively short adaptation time.
• The dynamic curvature aftereffect is similar to previously reported static curvature aftereffects (Van der Horst et al., 2008; Vogels et al., 1996).

4.2. Dynamic touch versus static touch

• One of the most important findings of this study is the complete intermanual transfer of the dynamic curvature aftereffect.
• Since the immediate contact of a single finger is insufficient, curvature information must be derived from the dynamic contact between the finger and the stimulus surface.
• The point of contact is displacement is too small to provide sufficient information.
• The remaining sources cannot individually provide information about the shape of the stimulus, since they are indistinguishable for convex and concave shapes.

4.3. Active dynamic touch versus passive dynamic touch

• Intermanual transfer of the aftereffect was found for both active and passive dynamic touch.
• In the previous section, the authors argued that information about the direction of movement is essential to distinguish a weakly curved shape.
• The correspondence between these findings is that a smaller aftereffect was obtained when the test stimulus was touched passively instead of explored actively.
• A related aspect is that active and passive dynamic touch require different sensorimotor involvement.
• Following adaptation to a convex shape to convex curvature information, the pressure profile of exploring a flat surface corresponds to that of a slightly concave surface without adaptation.

4.4. Conclusion

• The current study demonstrates the existence of a haptic dynamic curvature aftereffect and a complete intermanual transfer of this effect, which suggests that dynamically obtained curvature information is represented at a high level in the brain.
• A comparison between active and passive dynamic touch shows a larger aftereffect for actively tested curvature.
• In conclusion, this study provides evidence that the representation of object information depends on the exploration mode that is used to obtain that information.
• The definition of passive dynamic touch as used in the current study differs from the more strict definitions of passive touch, in which there is no role for the efferent commands (Chapman, 1993; Loomis & Lederman, 1986, chapter 31).

Figures

Fig. 3. (a) Mean results of the aftereffect for eight subjects. The error bars represent th explored by self-induced exploration with the index finger. In the passive conditions, the the conditions in which the adaptation and test stimuli were touched by the same index fi stimulus was touched by the right index finger and the test stimulus was touched by the active–passive condition, the adaptation stimulus was explored actively, while the test sti the adaptation stimulus was followed by active exploration of the test stimulus.

Fig. 2. Examples of two psychometric curves of one subject in an active, samefinger condition. The response is plotted against the curvature of the test stimulus. The psychometric curves were obtained by fitting cumulative Gaussians to the data. The circular data points represent the response when adaptation was performed with the convex adaptation stimulus; the square data points result from adaptation with the concave adaptation stimulus. The points of subjective equalities are given by PV and PC, respectively. The magnitude of the aftereffect (AE) is defined as the difference between PV and PC.

Fig. 1. Experimental setup. The arms rested on a support that was 19 cm above the tabletop. The stimuli were placed in slits on a platform, which was 14 cm above the tabletop. Thedistancebetween the centresof the slitswas40 cm. In this example, the subject explores the concave adaptation stimulus with the right index finger before touching the test stimulus with the opposite index finger. In the active conditions, the stimuli remained in a fixed position; in the passive conditions, a computer controlled steppingmotormoved the platform. The surface of the stimuli was circularly curved. The length of the stimuliwas 200mm, and thewidthwas 20mm. The height at the side of the stimuli was 40mm.

Fig. 4. (a1) Illustration of convex and concave stimuli in contact with a single finger by st indentation profile on the finger. (a2) Static touch with different parts of the hand that co each contact point must be combined with information about the position of the finger in information sources when there is dynamic contact between the finger and a stimulus. (b1 The deformation depends on the direction of movement contact, as indicated by an arro (rotation), when the finger moves over the stimulus surface. In the example, the finger rem on the finger does not change. Besides, the finger displaces in the vertical direction, but th of the finger with respect to the stimulus surface can change when the finger moves ove finger does not rotate.

Frequently asked questions

Q1. What contributions have the authors mentioned in the paper "Transfer of the curvature aftereffect in dynamic touch" ?

Van der Horst et al. this paper investigated the transfer of curvature aftereffect when curved surfaces were explored dynamically by a single finger. 

Q2. What have the authors stated for future works in "Transfer of the curvature aftereffect in dynamic touch" ?

This finding raises interesting questions about the importance of self-induced movement in dynamic touch, which might be the subject of future studies.