Effects of transmission delay on conversational behavior on echo-free telephone circuits

The present study sought to determine the effects of echo-free transmission delays of 600 ms and 1200 ms on conversational behavior when subjects were unaware that delay was present. Sixteen pairs of male subjects conversed 10 minutes each over an echo-free telephone circuit with zero delay and 10 minutes each with 600 ms round-trip delay; a second group of 16 pairs conversed 10 minutes each on zero delay and 1200 ms round-trip delay. Subjects noticed nothing unusual about the circuit, but the delay caused a statistically significant increase in frequency of confusions and in amount of both double talking (simultaneous speech from both speakers) and mutual silence. Analysis by means of an on-off pattern generating model revealed that subjects seem to make some adjustments in their speaking behavior; they tend to wait longer for responses and keep talking longer when interrupted. The two delay values of 600 ms and 1200 ms produced virtually identical effects in the measures made here. All of the subjects in the study were inexperienced with delay circuits; this experiment does not address itself to the possibility that experienced subjects might react differently to the delay. Further work will investigate the effects of training subjects to notice delay.