Final answer:
In Broadbent's model of attention, relevant messages are identified at the filter. The filter selects stimuli based on physical characteristics before allowing them to reach the detector for further processing. This mechanism serves to prevent irrelevant information from overloading short-term memory.
Step-by-step explanation:
In Broadbent's model of attention, relevant messages are identified at the filter. This model suggests that sensory information first reaches what is known as a filter, where the most salient stimuli are selected based on certain physical characteristics, such as the pitch of a sound or the brightness of a visual stimulus. Once filtered, only the chosen information reaches the detector, where it is then processed for meaning and subsequently may pass on to short-term memory, if deemed important.
In contrast to options a and b, not all messages make it through to the detector or short-term memory; only those which have been selected by the filter. Option c accurately describes Broadbent's theory, including the concept that irrelevant sensory information is discarded before it can clutter short-term memory with unnecessary data.