In the Marcel experiments, if subjects not confident they definitely saw something, they may say “no” on every trial.
=> discrimination performance = 50%
But if subjects are forced to respond yes 50% of time, maybe they would be above chance?
Maybe Marcel had not found the objective threshold for discrimination?
Cheesman & Merikle presented subjects with one of four colour words (“red”, “green”, etc). On each trial, subjects had to say which word had been presented.
(Now even if subjects believed they saw nothing, have to guess something.)
After each block of 40 trials, the SOA was reduced until subjects were performing at chance.
After each block of trials, subjects estimated how accurate they had been.
- If they felt they had no information whatsoever, they were just guessing purely randomly, subjects gave an estimate of 25% correct (=chance expectation).
If they were certain, they would give an estimate of 100%.
- Subjects could give any value between 25% and 100%.
Objective threshold = the SOA at which subjects really are performing at chance.
The subjective threshold is reached at a higher SOA than the objective threshold.
the two thresholds are different
Stroop priming is obtained for colour words presented below the subjective threshold, but NOT below the objective threshold.
Conclusion: BOTH results indicate unconscious processing below a subjective threshold.
But no evidence for unconscious processing below an objective threshold.
Research since then has confirmed it is easy to get unconscious perception below a subjective threshold, but very difficult below an objective threshold.
Greenwald (1992) found that 93% of the cognitive psychologists he surveyed regarded subliminal perception as having been demonstrated below a subjective threshold.
Is the subjective threshold just a curiosity or theoretically interesting?
Need to establish qualitative differences between knowledge above and below the subjective threshold.
Merikle & Joordens (1997)
Only two words used: Red/green.
“Red” or “green”
&&&&& (in red or green ink)
Task: Name colour of ink.
On 75% of trials, the prime and target were incongruent (e.g. “red” followed by green ink)
And 25% of trials congruent
A conscious belief (e.g. “I am seeing the word RED”) can be combined with any other belief or desire to which it may be relevant in order to produce further beliefs or actions (in this case, to be prepared for green ink).
Unconscious knowledge cannot combine with just any other possibly relevant belief or desire to plan action.
=> Only conscious knowledge is inferentially promiscuous.