Early filter models: Broadbent (1958)
The bottleneck occurs early in the system.Tested by a dichotic listening task:
- 3 digits presented diachotically and presented one after the other to one ear at the same time as three different digits were presented to the other ear.
- Most participants preferred to recall the digits ear by ear rather than pair by pair.
How did the task account for the various findings?
1) 2 stimuli or messages presented at the same time gain access in parallel (at the same time) to a sensory buffer.
2) One of the inputs is then allowed through a filter on the basis of its physical characteristics, with the other input remaining in the buffer for later processing.
3) This filter prevents overloading of the limited capacity mechanism beyond the filter, which processes the input thoroughly (e.g. in terms of meaning)
It handles Cherry's basic findings, with unattended messages being rejected by the filter and thus recieving minimal processing.
It also accounts for performance on Broadbents' dichotic task: The filter selects one input on the basis of the most prominent physical characteristics distinguishing the two inputs (i.e. the ear on arrival).
Evaluation of Broadbents Theory (1958)
- Assumption is dubious - i.e. information rejected at an early stage.
- The study used participants with very little experience of shadowing messages to nearly all their available processing resources had to be allocated to the shadowing.
- Underwood (1974): Found that naive participants detected only 8% of the digits on the non-shadowed message but an experienced researcher in area detected 67%.
- Allport, Adonis and Reynolds (1972): Degree of similarity between the two messages had a major impact on memory for the non-shadowed message. This increased to 90% when combined with pictures.
- Inflexible system of attention - cannot account for great variability in the amount of analysis in the non-shadowed message.
- Grey and Wedderburn (1960): Selection not necessarily based on physical characteristics.
What is Deutsch and Deutsch's (1963) model?
- It is a late filter model - all information from both channels is attended and processed semantically.
- Irrelevant information is filtered out at the time of STM storage (i.e. why it is a late filter model).
- Both channels are processed to the same degree, only the most relevant channel to the task at hand is responded to.
- This accounts for how sometimes information from the unattended channel can break through and be processed for meaning.
What is Treisman (1964)'s Attenuation Theory?
- Treisman retained an early filter that distinguishes information on physical differences (like Broadbent's theory). However, rather than eliminating the unattended material, Treisman's theory attenuates it (turns it down).
- Location of the bottleneck is much more flexible than Broadbent had suggested.
- Accounts for findings such as hearing your own name in an unattended channel (Conway, Cowan and Bunting, 2001).
- Stimulus analysis proceeds systematically through a hierarchy - starts with analyses based on physical cues, syllable pattern and specific words, and moving onto analyses based on grammatical structure and meaning.
- If there is insufficient processing capacity to permit full stimulus analysis, tests are towards the top of the hierarchy.
- Thresholds of all stimuli consistent with current expectations are lowered. Partially processed stimuli on the unattended channel sometimes exceed the threshold of conscious awareness. Helps to account for the breakthrough.
- Accounts for the extensive processing of the unattended sources of information that was embarassing for Broadbent.
How did Treisman (1969) test his theory?
- Participants asked to shadow message in one ear, but then they had to tap when they heard a target word from any source (either ear).
- Attenuation model: More targets should be reported from the shadowed stream than the unattended stream.
- Late filter model: Equal numbers of words should be detected from each stream
- Results: Many more words were detected in the attended stream relative to the unattended stream, supporting Treisman's attenuation theory.