Attention is viewed as the process of selecting some of the many available inputs. There are certain theories proposed by different psychologists on how this selection takes place. In this session we are going to learn about Broadbent’s filter theory.

Broadbent’s theory is one of the earliest theories of attention. Broadbent assumed that an individual's attention capacity is limited, and that when the information flow is too great, we simply block some of the information. According to this filter theory, whatever is not attended to, is simply lost.

As shown in the figure, we filter information right after it is registered at the sensory level (Broadbent, 1958). This is therefore an early selection theory.

In Broadbent’s view, multiple messages of sensory input reach an attentional filter. The filter operates on the basic physical characteristics of the messages (e.g. gender of the speaker, type of sound). This means that information is not processed semantically (for meaning) until after it has been selected for attention. It permits only one message of sensory information to proceed through the filter to reach the processes of perception. We thereby assign meanings to our sensations. Other stimuli will be filtered out at the sensory level. They may never pass through the attentional filter to reach the level of perception.

To better understand the filter in Broadbent’s theory, think about a sieve at use at the beach. A sieve lets through fine sand only trapping the coarse grains of sand, based on the physical characteristics of the sand particles (size in this case). Broadbent’s attentional filter lets through the attended message and keeps the unattended message from getting through, based on physical characteristics of the message, such as the pitch of the person’s voice.

Broadbent came up with the theory based on data from an experiment where three pairs of different digits are presented simultaneously, three digits in one ear and three in the other. Most participants recalled the digits ear by ear, rather than pair by pair. Thus, if 4, 9 and 6 were presented to one ear and 8, 5 and 2 to the other, the recall would be 496 852 (ear-by-ear) rather than 48 95 62 (pair-by-pair).