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Top1. Introduction
In text-based communications over a computer, users naturally understand that there is a certain time lag between sending a text message and receiving a reply. With the release of mobile phones that support internet access, users began to utilize mobile phones for text-based communications as well (Faulkner & Culwin, 2005; Harrison & Gilmore, 2012; Lin & Tong, 2007). As cell-phone textual interactions became popular, faster speeds were needed for cell phone exchanges than for PC-based communication (Angstermichael & Lester, 2010; Battestini, Setlur, & Sohn, 2010; Reid & Reid, 2007; Skierkowski & Wood, 2012). One reason might be that mobile phones are recognized as part of the owner’s body. Nevertheless, in cell-phone text messaging, a sender’s imagined explanation for why a recipient does not immediately reply is based on empirical or circumstantial cues (Kato & Kato, 2015; Kato, Kato, & Chida, 2013; Tyler & Tang, 2003).
In Japan, many people now own smartphones. In addition to cell-phone text messaging, social networking/social media apps are also widely used on smartphones (e.g., Ahad & Lim, 2014; Church & Oliveira, 2013; Pew Research Center, 2016). According to a 2016 survey of Japanese young people (Ministry of Internal Affairs and Communications, Japan, 2016), the most used social networking application is LINE, which has various functions, including call and text messaging. In this study, we focused on LINE text messaging (hereinafter simply “LINE”). LINE is an instant messenger similar to other internet-based messengers such as WhatsApp. However, due to its high operability, LINE in Japan is typically used as a daily textual communication alternative to traditional cell-phone text messaging rather than as an instant messenger (Kato, 2015; Kato, 2016). Although LINE can easily exchange text messages, its users typically expect faster reply speeds than in cell-phone text messaging. In fact, the act of periodically checking one’s smartphone for incoming messages has become a daily occurrence. One explanation is the read receipt function of LINE as described below.
LINE’s read receipt function, which was originally implemented to confirm the safety of people affected by the 2011 Great East Japan Earthquake, automatically informs the sender that the recipient has read the message. According to Kato (2016), today’s users generally recognize that the function of the read receipt is to notify the sender that the recipient is in a position where they can use their smartphone and their reply will arrive shortly. However, the sender must manually open LINE to check if a read receipt is available, even if the recipient has not yet checked the message. In situations where the recipient “reads” the message but cannot yet reply, there might be some time between the read receipt displaying and the actual reply arriving, which may lead the sender to feel suspicious at this time lag. At the same time, a recipient who feels pressure to reply immediately might then hesitate to open the message, thereby. Thus, LINE’s read receipt would appear to strongly influence the speed at which exchanges take place through LINE.