Harry R. Schwartz

I’ll often make little “uh-huh” or “mmm-hmm” or “oh, sure” noises while carrying on a conversation. They indicate that I’m still listening to the speaker and paying attention. If I didn’t make those little noises they might assume I’d stopped listening and was ignoring them.

Linguists refer to these sorts of terms as phatics.¹ From an information theoretic perspective they indicate that the channel of communication remains open and that the receiver is still accepting messages. They’re not quite the same as an ACK, which indicates that a specific message has been received; it might be better to think of them as periodic heartbeat notifications from the receiver.

Phatic messages occur all the time in human-computer interactions! If you leave most desktops alone long enough they’ll dim or lock the screen, or maybe start a screensaver, since they reasonably assume that you’re no longer paying attention. To indicate that you’re still there you might wiggle the mouse every now and then, the GUI equivalent of “mmm-hmm.”

Another example might be a bank’s site that logs you out after a certain amount of inaction. It’s not getting any phatic messages from you to indicate that you’re on the other end of the communication channel, so it closes that channel.

These phatic interactions are another idea I found in Gerald Weinberg’s delightful 1971 book, The Psychology of Computer Programming. His examples are older than mine, of course, but they describe the same sort of phenomenon:

An exact counterpoint to the phatic “and” is found in some terminal systems where the user can keep his program from being pushed down in the priority stack by fiddling with the shift key while he is thinking. Without the shifting, the computer would fail to get a communication for a long period and assume that the user’s program could safely be put in a more passive state.