Comprehension was measured using subjective judgments by subjects concerning the percent of thoughts contained in the passages that they estimated they understood. This measure had previously been demonstrated to be a valid, reliable method of measuring comprehension (Carver, 1973a).

The objective number of thoughts in each passage was specified operationally as the number of standard-length sentences in each passage, with a standard-length sentence defined as 16 five-letter words. For the study under discussion, the passages presented for auding and reading contained an average of 20.8 standard sentences. To calculate the rate of presentation of messages in standard sentences per minute (SSPM), 20.8 was divided by the time needed to present the messages at each of the rates from 75 to 450 wpm. This number Carver called the information presentation rate. The percent of these standard sentences which subjects estimated they understood was used to index the information storage rate. One question raised, then, is whether subjects store information as fast as it is presented, or is there some optimal rate of storage which, when exceeded by the presentation rate, results in decreased storage. A second question is whether auding and reading might differ in regard to optimal information storage rates, if such are found.

Figure 7 presents data adapted from Carver's report. There appears to be an obvious optimum for auding between 15-20 SSPM or 240-320 SWPM. These data are consistent with the data regarding speed auding reviewed earlier. The apparent lack of an optimum for reading storage rate reflects the methodology used to manipulate reading rate in which only the time for reading was manipulated, not the actual rate of appearance of the printed information. The reading data reflect the fact that subjects were told to read at their normal rates. Thus, with less time to read subjects learned less material. But since both time and amount read decreased together, the ratio formed by dividing amount read by time to read it stayed constant at nine standard sentences per minute. This suggests that students were presenting information to themselves by reading at an average rate d 16-19 SSPM, or 250-300 SWPM-rates comparable to the optimal rates found for auding. If we assume that students typically read at rates which they feel are optimal for them, then we may conclude that auding and reading showed comparable optimal rates.