Subjects were presented dichotically with pairs of digits and were instructed to shadow whichever message they preferred. A strong preference was shown for attending ear-by-ear. Broadbent theorised that stimuli are selected according to their physical attributes and unattended messages are not semantically processed and discarded. According to Broadbent, switching attention from one stimulus to another is also quite difficult. .

             These two previous experiments had numerous weaknesses. In Cherry's experiment subjects were asked about information in non-shadowed messages after they had completed the shadowing phase. This information may have been perceived and processed, but forgotten later. In Broadbent's experiment there was no particular meaning to be extracted from the pairs of digits presented, so there was no sufficient evidence to draw conclusions about semantic processing. Moreover, it was later made clear that it is possible to easily switch attention from one ear to another, when the meaning of the unattended message was relevant to the shadowed message.

             Experiments by Grey and Wedderburn (1960, in Parkin, 1999) and Treisman (1964, in Parkin, 1999) demonstrated that subjects select which message to attend to by following the meaning of a sentence. This suggests that humans can select a stimulus according to its meaning not only its physical cues. This could directly provide evidence for a late-selection model. However, Treisman (1960, in Kahneman and Treisman, 1984) accounted for this finding with the 'attenuator' model, which is still an early selection theory. She proposed that the filter described by Broadbent is actually more flexible and the unattended message can be partly semantically processed. Treisman's attenuation theory was a good alternative to the filter model, as it could explain the new findings. However, it has been criticised for lack of clarity and for being a half-measure.