Taken last, selected first: The sampling bias is also present in the haptic domain

Atten Percept Psychophys (2015) 77:941–947 DOI 10.3758/s13414-014-0803-3 Taken last, selected first: The sampling bias is also present in the haptic domain Takashi Mitsuda & Yuichi Yoshioka Published online: 3 December 2014 # The Psychonomic Society, Inc. 2014 Abstract When people are presented with a pair of images and asked to identify which one is more attractive, their eye gaze shifts gradually toward the image that they eventually choose. This study examined whether this sampling bias also occurs in other sensory modalities by observing participants’ behavior in a haptic preference task. The results indicated that the participants tended to sample the chosen item just prior to making their decision when they were instructed to identify their most preferred item (i.e., the “like” task), but not when they were instructed to identify their least preferred item (i.e., the “dislike” task). This indicates that the sampling bias is a general phenomenon regardless of sensory modality. In addition, the sampling bias in the like task was larger when the difference in preference ratings between the paired items was smaller. However, the sampling bias decreased when the two items were given equal preference ratings, despite there being a longer decision time on those trials. This suggests that the sampling bias is not simply related to task difficulty, but is also related to preference formation and/or selective encoding of task-relevant information. Keywords Gaze bias . Preference . Haptic . Tactile sense . Decision making . Dislike Introduction Making choices between multiple items is a fundamental activity in daily life. For example, when selecting a blouse to purchase in a shop, people usually examine and compare the various candidates repeatedly. Shimojo, Simion, Shimojo, T. Mitsuda (*) : Y. Yoshioka College of Information Science and Engineering, Ritsumeikan University, 1-1-1 Noji-Higashi, Kusatsu, Shiga 525-8577, Japan e-mail: and Scheier (2003) have shown that this looking behavior is related not merely to item evaluation, but also to preference formation. These latter authors tracked the eye movements of individuals who were shown pairs of human faces and asked to decide which face was more attractive. The results showed that participants’ eye gazes were initially distributed evenly between the two stimuli, but approximately 1 s prior to making a decision, they gradually shifted their eyes toward the face they subsequently chose. However, this “gaze bias” was significantly weaker when the participants were asked to select the less attractive, or the rounder, of the two faces. As a result of this study, looking behavior in preference-judgment tasks has been well researched in the literature (Glaholt & Reingold, 2009; Krajbich, Armel, & Rangel, 2010; Mitsuda & Glaholt, 2014; Nittono & Wada, 2009; Schotter, Berry, McKenzie, & Rayner, 2010). Although the source of the gaze bias is still being debated, there is evidence indicating that it is not a response-related phenomenon; rather, it may be related to the decision-making process. Recently, Lindsen, Gurpreet, Shimojo, and Bhattacharya (2011) showed that the behavior of sampling musical excerpts was also biased when participants were asked to choose an excerpt that they liked, but not when asked to choose one they did not like; thus, the observed bias was similar to the gaze bias. These results indicate that these types of biases could be a general tendency in preference-judgment tasks, regardless of the sensory modality. To the best of our knowledge, Lindsen et al. (2011) is the only study that has investigated the sampling bias in preference-judgment tasks in sensory modalities other than vision. Accordingly, we tested whether the sampling bias also exists in the sensory domain of tactile processing. The present study introduced a two-alternative forcedchoice task that asked participants to indicate their preference for handkerchiefs—a common activity in daily life. We expected that the sampling bias would be larger when the 942 participants had to choose the handkerchief that they liked the most than when they had to choose the one they disliked the most, in accordance with the visual-preference and musicalpreference task literature discussed above. The present study also analyzed the relation between the sampling bias and task difficulty (i.e., the difference in preference level) in order to investigate the role of the sampling bias in the decisionmaking process. In previous studies, the gaze bias in a visual preference task was larger for the more difficult task (i.e., the difference in preference level was small; Shimojo et al., 2003). This indicates that the gaze bias is not merely a tendency to look at the chosen item, but rather is related to the decisionmaking process. Thus, we expected that the sampling bias in the haptic preference task would be larger for the more difficult task. Atten Percept Psychophys (2015) 77:941–947 The participants performed 15 trials in the like task and 15 trials in the dislike task on separate days, and task order was counterbalanced across participants. The entire experiment was completed in approximately 50 min each day. The 30 handkerchiefs were paired randomly for each participant and task. The participants did not judge the same handkerchief more than once in either task. Their behavior was recorded by a video camera. The beginning and end of a trial was determined by watching the videos. The time resolution of the video was 0.1 s. We defined the beginning of a trial as the time of the first touch and the end as the time when the dominant hand was placed between the handkerchiefs. Repeatedly touching the same handkerchief was regarded as one sample when determining the amount of sampling per handkerchief. Experiment 1 Results Method Participants Twenty-eight male students at Ritsumeikan University aged 21–25 years (M = 21.9, SD = 1.3) participated voluntarily in the experiment. This experiment was approved by the local ethics committee. Materials Thirty handkerchiefs that differed in texture or weave were used for the experiment. Two handkerchiefs were presented 30 cm apart inside a box in front of the participants. The handkerchiefs were covered by the box, so the participants could not see them. The handkerchiefs differed in tactility. They were made of cotton, silk, hemp, artificial fabrics, terrycloth, etc. Some of them had embroidery, which provided a different tactile sensation. Procedure We monitored hand movements when the participants were presented with a pair of handkerchiefs and asked them to identify the one they preferred the most or least. The participants were instructed to touch the handkerchiefs one at a time with their dominant hand. The experimenter told the participants which handkerchief to touch first at the beginning of each trial (i.e., “touch the right handkerchief first,” or “touch the left handkerchief first”) in an alternating order. T (...truncated)