Selective Attention: Perception or Response?

Does our limited capacity in selective listening tasks arise primarily in perception or in response organization? To examine this, subjects were given two dichotic messages, one primary and one secondary, and had to make two different responses: the primary response was to “shadow” the primary message; the secondary response was to tap on hearing certain target words in either message. Since the secondary response was identical for the two messages, any difference in its efficiency with the two messages must be due to a failure in perception of the secondary message. Any interference between the primary and secondary responses (repeating and tapping) to target words in the primary message must be due to a limit in performing simultaneous responses, since if either was correctly performed the target word must have been perceived. The results clearly showed that the main limit is perceptual. Various target words were used to investigate the nature of the perceptual and response limits. Factors investigated were (1) the information content of the target words, (2) their range of meanings, (3) their grammatical class, and (4) the compatibility between stimuli and responses. A relative lack of response competition was found, which might be due to successive organization of the two responses at different stages in the perceptual sequence. The results were interpreted in terms of signal detection theory and the effects of reduced signal-to-noise ratio produced by inattention were compared with those produced by an external masking noise.