## 4 Discussion  
How would we perceive a physical contact by a robot? Would we consider it (non)threatening? Would we find it (dis)comforting? These are among some of the most basic questions to seek answers for if the robots are to ever take part in our social life activities [41; 42]. The present research investigated these questions by examining whether the background information about the level of autonomy of a robot would have any effect on its perception by individuals whom it made a physical contact with. For this purpose, we asked 30 young adults to let a robot-arm touch their left arm in two consecutive trials. While the robot was autonomous and used exact same program for its movement in these two trials, we told our participants that in one of their trials the robot was controlled by a human operator while in the other the robot moved autonomously. We observed that the participants' gender and personality traits had no influence on their perception of robot-touch. This discarded the overemphasis of gender [28] during interaction with robots. In the same vein, the gender of (sham) human operator (whether female or male) did not play a role in participants' perception of their two trials. A number of previous studies [43; 44; 45] reported that, in various cultures and countries, men and women both preferred a touch by women more than by men. In light of these findings, the non-significant effect of operator's gender in the present study indicated that the participants did not attach any social component to the robot-touch. On the other hand, we observed that although the robot-touch was identical in both trials, participants significantly preferred the trial that was supposedly operated by a human. This extended the previous findings on humans' disapproval of soft/algorithmic agents [20; 21; 22; 25] to the case of physcial contact with a robot. It also complemented these findings by showing that in spite of identical tasks, a minor manipulation of the agent's identity was sufficient to reproduce these previous findings. However, the more important (and perhaps pressing) observation in present study pertained to the effect of trial-order on participants' comfortability with the robot-touch. Concretely, we observed that the participants significantly preferred their first trial, regardless of whether it was a robot- or a (sham) human-controlled scenario. This highlighted a sensitization effect: a component of nondeclarative memory [46] (p. 390) which refers to the type of knowledge that an individual is not conscious of. Types of memory that fall under this category include: procedural memory [47] (e.g., learning complex repeating patterns that appears as random), priming [48] (e.g., change in the response to a stimulus or the ability to identify that stimulus, following a prior exposure to that stimulus), conditioning (e.g., [PERSON] dog), habituation (e.g., getting used to an initially uncomfortable toothbrush) and sensitization (e.g., rubbing one's arm which, at first, creates a feeling of warm but when continued it starts to hurt [46] (p. 395)). Interestingly, we also observed that the change in participants' salivary cortisol did not differ significantly. The presence of sensitization along with the non-significant change in salivary cortisol indicated that the observed effect was not due to different degree of stress or anxiety in two trials but primarily triggered by participants' memory of the event. As a form of nonassociative learning, sensitization (and its closely related effect; habituation) primarily involves sensory and sensorimotor pathways [46] (p. 395). However, contrary to habituation which reflects an incremental level of comfort over time, sensitization signals increased sensitivity and loss of comfort. As a result, the observed memory sensitization among participants in the present study indicated their growing distance toward robot-touch. In other words, it signified how these individuals (uncsonciously) felt (i.e., their emotional stance) about the robot-touch itself.