Why do potters make shorter vessels on the wheel when one or two of their modalities are reduced? Mounia Ziat1, Min Kyung Park1, Brian Kakas1, and David Rosenbaum2 1Northern
Michigan University, Marquette, MI, 49855 State University, State College, PA 16802
[email protected]
2Pennsylvania
Abstract. When asked to shape a cylindrical vessel on the potter’s wheel, potters make shorter pots when one or two of their modalities are reduced than when all their modalities are available. This outcome may reflect a tendency to maintain control over the pot while the wheel is rotating. Keywords: Pottery, Multimodal Integration, Manual control
1
Introduction
Our interaction with the world relies on several sensory inputs that allow the perception of surrounding objects in a stable fashion [1, 2, 3, 4]. A useful way to investigate the integration of inputs from different sensory modalities is to observe the effects of withholding one or more of those inputs. We pursued this approach in a series of experiments in which we observed potters shaping a cylindrical vessel when one or two of their modalities were reduced. The choice of potters is no accident since hands are as important as eyes, if not essential to produce the artistic piece. What was less obvious, and was revealed by these two studies, is that the auditory feedback also provided potters with relevant information while shaping the vessel on the potter’s wheel.
2
Experiments I and II
Participants Twenty-four participants took part in each experiment. They were all ceramics students from Northern Michigan University who gave their informed consent before participating. The procedures were approved by the Institutional Review Board. 16 females and 8 males (mean age = 24, SD = 7.97) participated in experiment 1 and 19 females and 5 males (mean age = 24, SD = 10.6) participated in experiment 2.
Apparatus and Task All participants used a Brent model C pottery wheel (Figure 1). The 14 in aluminum wheel head was fitted with a 12 in throwing bat. This model has a permanent magnet ¾ hp, 7 amp DC motor, which offers a smooth speed range of 0-240 rpm. Participants were all given a pugged cylinder of stoneware clay of 680.39 g (1.5 lbs). A gallon bucket of water and small sponge were also provided. The task was to shape a 5 in tall cylindrical vessel, which is the first type of form to which beginner potters are exposed. All participants were familiar with the apparatus and shaping a cylinder. Therefore no training was required.
Fig. 1. Left) A potter shaping a vessel on the wheel, Right) Diameter and height of the vessel
Procedure Ceramic students were asked to shape the clay and were divided into three groups (modality conditions) named on the remaining modalities used to shape the vessel. • Experiment 1: 1) participants in group AH (Auditory-Haptic) were blindfolded to remove the visual input, 2) participants in group VH (Visual-Haptic) wore earplugs and headphones with a NRR of 62dB to prevent them from hearing the sound produced by the potter’s wheel, and 3) participants of group AV (Auditory-Visual) wore Nitrile gloves of 15 mil (0.381 mm) that significantly reduced the cutaneous contact with the clay. • Experiment 2: 1) participants in group H wore blindfolds, earplugs, and headphones to block vision and reduced audition, 2) participants in group V wore gloves, earplugs, and headphones to reduce both haptic and auditory inputs, and 3) participants in group A wore gloves and blindfold to only used the auditory feedback. All participants shaped a vessel under two conditions: a control condition where none of the senses has been altered and a test condition where one or two of the three senses has been reduced. The conditions have been randomized across participants.
3
Results
Experiment I The results showed that the potters succeeded in shaping the vessel despite the deprivation of one of their sensorial modalities. A two-way mixed ANOVA with repeated factor height showed a significant effect between both test and control conditions [F(1,
21) = 5.83, p = 0.025]. As shown in Figure 2, height was always underestimated when one of the three modalities was attenuated or removed. Although there was no significant effect for the modality factor, the effect was more important for V and H conditions. Finally, potters seems to make shorter pots than the requested height (5 in).
Fig. 2. Left) Average height for the three conditions: HV (auditory reduced), AV (haptics reduced), AH (visual removed). Right) Percentage of underestimation for the three conditions.
Experiment II
Fig. 3. Left) Average height for the three conditions: V (auditory and haptics reduced), A (haptics and visual reduced), H (visual and haptics removed). Right) Percentage of underestimation for the three conditions.
Similarly to experiment I, the same trend was observed for experiment 2. The only significant effect was related to height [F(1, 21) = 15.21, p = 0.001]. While the effect of the modality factor was not significant, it is also seen in Figure 3 that the underestimation for the H-only modality is more important (%19) that A and V only modalities (11% and 12% respectively).
4
Discussion and Conclusion
The results showed that when one or two modalities are reduced, potters tend to make shorter pots. A way to interpret this outcome is to note that the throwing process is one of combatting centrifugal force by applying enough pressure while the wheel is rotating to keep the clay from flying off while avoiding applying too much pressure that could
crush or distort the desired shape of the emerging tube. To shape a cylindrical vessel, potters must proceed in four steps: 1. Wedge the clay: Once a lump of clay is placed on the wheel, it needs to be firmly secured to start the centering process. 2. Center the clay: Potters attempt first to shape the cylinder while maintaining the clay in the center. This task is difficult for beginners as the key is to modulate the right amount of pressure to keep the clay in the center to prevent it from flying off the wheel. 3. Establish a base: Once centering is successfully achieved, potters press with their two thumbs the center of the cylinder to form the aperture of the vessel. Determining the diameter is obtained by forming an enclosure with both hands around the cylinder and by applying the right amount of pressure. 4. Bring up the walls: Height is fixed by pressing the border with the right hand (outside to inside), while the left hand is used to lead and support the interior side. Proprioceptive and force feedback are heavily involved in the process. More specifically resistance force from the wheel provides information about the clay position relatively to the wheel. While resistance force from the wheel is constantly present in the three first steps informing the potter about the diameter and height, its effect is negligible in the last and fourth step where the only available information comes from proprioception and the clay. Because potters receive less information during this phase, crucial in determining the height of the vessel, they decide to stop building up the walls to maintain control over the shape. The taller the pot, the more difficult it is to maintain a stable diameter at the top because of the centrifugal force. To confirm this explanation, we would like to compare performances of experienced and beginner potters. The results of both experiment also suggest that in order to estimate the height accurately, all the three modalities need to function together. It is possible that height is a multimodal feature for potters and requires the presence of the three modalities to be accurately estimated. We are planning to ask potters to estimate the height of already made pots while one or two modalities are reduced to confirm this hypothesis. Finally, since the role of proprioception is crucial, we would like to disturb the kinesthetic feedback during the throwing phase by placing vibrations on the cubital fossa (elbow pit).
References 1. Frissen, I., Ziat, M., Campion, G., Hayward, V. and Guastavino, C. The effects of voluntary movements on auditory–haptic and haptic–haptic temporal order judgments. Acta psychologica, 141(2), pp.140-148, (2012). 2. Spence, C., Pavani, F. and Driver, J. Spatial constraints on visual-tactile cross-modal distractor congruency effects. Cogn., Affect., & Behav. Neuro., 4(2), pp.148-169, (2004). 3. Ziat, M., Balcer, C. A., Rolison, T. and Shitz, A. A century later, the hue-heat hypothesis: does color truly affect temperature perception? Eurohaptics 2016, (2016). 4. Ziat, M., Frissen, I., Campion, G., Hayward, V. and Guastavino, C.. Plucked String Stiffness Affects Loudness Perception. In Haptic and Audio Interaction Design, pp. 79-88, (2013).
