Class 3, Lecture 6, Chapter 4: Paying Attention
Other studies of attention focus on a phenomenon known as change blindness, the
inability of observers to detect changes in scenes they are looking directly at.
See if you can detect the differences between the following pairs of pictures:
Similar effects of change blindness occur when people fail to notice continuity errors
In a particularly striking example, participants failed to notice when the person asking
them for directions changed identity (following a brief interruption by two people
carrying a door).
Early studies of attention focused on when the perceiver selects the desired input.
According to the early-selection hypothesis, the unattended input receives little to no
o based on
According to the late-selection hypothesis, all input receives analysis but only the
attended input reaches consciousness or is remembered.
o Things with meaning are picked up indicating that it has to be processed with
meaning before processing on it is stopped.
Both the early- and late-selection hypotheses capture part of the truth.
o For instance, the study discussed earlier showing that unattended stimuli have
effects on perception seems to be a case of late selection.
The idea that we process things up to a level of meaning and pay
attention to what we select up to
o However, the electrical activity of the brain for attended versus unattended
inputs differs within 70 ms of stimulus presentation, suggesting early
Selection is occurring with 70 ms, brain activity is the same for
unattended and attended for up to 70 ms. After 70ms, there is a
difference in processing between the two.
It is only with those things that are high in meaning to us are
recognized early/quickly enough that they get to that level of meaning
before this 70ms level of change.
An experiment by Posner and Snyder (1975) illustrates that there are two kinds of
priming related to attention.
o One kind of priming is stimulus-based, the other is expectation-based.
Both speed up response times, top down and bottom up can produce
priming For this type of study, the dependent variable is the response time to make a decision
about the stimuli.
o Showed that priming can be turned “off” and “on”
Posner and Snyder (1975) found in the low-validity condition (the condition where
your prime wasn’t a good predictor of the next stimulus) that the primed condition
was faster than neutral.
o This demonstrates an effect of repetition priming; the receptors were “warmed
There was no expectation priming no expectation
But, the misled condition was not any slower than neutral.
o Warming up the “wrong” detector does not take activation away from the
o People learned to ignore that prime and not be affected by it, or were not using
it to their advantage
Posner and Snyder (1975) found in the high-validity condition that the primed
condition was much faster than neutral.
o This demonstrates an additional effect of expectation in addition to repetition
o Faster then the low validity because the individual was able to take the
stimulus cue and the meaning cue
Further, the misled condition was slower than the neutral condition.
o Expectation is limited in capacity; the “wrong” expectation interferes with
activating the correct detectors.
When they were expecting that prime to tell them what is coming next,
their response time was slower. Have the least advantage of priming
We only use expectation when it is valid
Studies of spatial attention examine the ability to focus on a particular position in
space and to be prepared for stimuli appearing in that position.
For example, when detecting a stimulus on the right or left side of the screen,
participants benefit if an arrow provides a cue indicating on which side the stimulus is
about to appear (Posner et al., 1980).
o They do this with eye trackers going, even when the eyes are not moving are
still able to move our attention
Note that directing spatial attention is different than moving the eyes.
Spatial attention is sometimes thought of as a “searchlight.”
We can move this searchlight in space, as well as adjust the size of the “beam.” o
Do we attend to positions in space or to objects?
Evidence from unilateral neglect syndrome, caused by damage to the right parietal
lobe, could be argued to support a space-based view. These individuals cannot attend
to the left side of space.
o Damage to the right affecting the left visual field contralateral processing
However, some experiments suggest that the deficit is also object-based.
Unilateral-neglect patients attended to the red circle, initially presented on the right,
even after it rotated to the left side of the object.
o In the beginning they could not attend to the circle in the left visual field.
o Only able to pay attention to the left visual field as long as they followed t