What Should We Observe?
You might think we could solve this problem simply by asking the conversers their opinions. We found out long ago, however, that the opinions you get are affected by a lot of things: how you ask the question, the attitude of the respondent, and his unrelated experiences outside the experiment. So we usually try a more subtle approach. In this case, my basic observation was of what psychologists call escape behavior. The conversers were told that they would start talking over a normal circuit, and that delay would be introduced at some point. (The delay was inserted in such a way that an abrupt change could not be noticed.) All the conversers had pushbuttons for signaling the experimenter. If they thought they noticed a delay, they were told that it would be removed if they pushed the button. Thus they could always escape from this possibly unpleasant condition.
My reasoning was this: If the conversers found it very difficult to talk with delay in the circuit, they would surely push the button soon after the delay was introduced. On the other hand, any time when they continued to converse without pushing the button—while delay was in the circuit—was obviously also a time when the delay did not make conversation impossible. So we had at least one measurable quantity—the time taken to detect delay—which we could interpret as an answer to our question. Note that we could tell if people pushed the button “just to be on the safe side” by seeing how often they did this when there actually was no delay in the circuit.
There are just a few more necessary details before we discuss the results:
- I recorded the conversations for later analysis, but the conversers knew that the recordings would be held in confidence.
- The amount of delay used was 1.2 seconds, which represents the total round-trip delay for a circuit using two satellites, including the delay in typical end connections on the ground. We used this much delay because our preliminary tests indicated that it would be more likely to produce an effect than would the 0.6 second delay in a one-satellite link.
- The entire 1.2 seconds of delay was put into one of the lines, since we had discovered that, where there is no echo, conversers cannot tell the difference between a delay of 2t seconds in one line and a delay of t seconds in each of two lines. I did this for the sake of convenience, so that I could introduce delay in the quiet line while the other one was active.
- After someone detected delay, I removed it immediately and then waited at least a minute before putting it back in.
- Altogether, I collected about two hours of conversation and introduced delay 22 times.
The Results and What They Mean
Now we could answer the question, “How long does it take people to detect 1.2 seconds of delay?” As you can see from [the table opposite], the times ranged all the way from 20 seconds to over 10 minutes, and, in two cases delay was not detected at all. The results in the table are also shown in the [histogram on the next page], which depicts how broadly the detection times were distributed. To me, one of the most interesting things is that even people who were able to detect delay quickly sometimes did not detect it for a couple of minutes. For example, the pair K/G had two times under a minute, one of 143 seconds, and one of 421 seconds. I interpret their two short times to mean that they knew what to look for, since they made no incorrect responses while delay was not present. However, their long times seem to mean that they sometimes didn’t notice delay for quite a while. Incidentally, only two responses were made during the total of about 40 minutes when I did not introduce delay, and these “false alarms” were by two of the fastest pairs at true detection—F/K and S/H.
Length of Time Before Seven Pairs of Talkers Could Detect 1.2 Seconds of Delay
| PAIRS OF TALKERS | NUMBER OF SECONDS BEFORE TALKERS DETECTED DELAY |
|---|---|
| G/H | 161 |
| 224 | |
| 107 | |
| F/K | 87 |
| 65 | |
| 43 | |
| 220 | |
| false alarm | |
| A/L | 618 |
| 95 | |
| 367 | |
| F/T | no detection after 954 seconds |
| S/H | 227 |
| false alarm | |
| 90 | |
| 75 | |
| 83 | |
| K/G | 38 |
| 421 | |
| 20 | |
| 143 | |
| S/W | 257 |
| 229 | |
| no detection after 260 seconds | |
