Running head: CHANGE DETECTION
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Cognition Full Lab Report- Change Detection
By:
Jason Thorpe
201102759
A laboratory report
presented to R.McInnis
in Psychology 220
Cognitive
Department of Psychology
St. Francis Xavier University
November 29, 2013
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Abstract
The basis of this experiment was to demonstrate that the human brain struggles to detect change.
Change detection is the process of depicting change from one sequence to the next. Forty-one
Saint Francis Xavier undergraduate students were asked to complete the change detection
experiment using Coglab. Participants were asked to analyze two photos to determine if a change
occurred by giving a response. In the condition with no flicker, participants demonstrated a mean
reaction time of 4537.945 milliseconds and were 0.958% correct. For the condition where a grey
flicker occurred, participants demonstrated a mean reaction time of 7860.907 milliseconds and
were 0.721% correct. In the end, we understand that humans suffer to detect change when a
disruption occurs to the individual’s concentration and attention.
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Cognition Full Lab Report- Change Detection
Change detection is the process of identifying differences in an object by observing it at
different times. The ability to detect change is an important aspect of our everyday life; examples
include, noticing a person walking, seeing oncoming traffic, or watching a child play around the
yard. The basis of this experiment was to demonstrate that the human brain struggles to detect
change. Essentially it relies on attention and how concentrated you are in the changed area. If
you know where the change is going to happen it is easy to distinguish. Studies have proven that
detecting change is a challenging process and one that we humans struggle with. For example,
observers tend to believe we could immediately detect any change in front of us if it was large
enough (Levin et al. 2000). However, this is not so. Under a wide variety of conditions we can be
blind to these changes even when they are significant. This situation is known as change
blindness. To demonstrate this, experimenters created short motion pictures where objects were
manipulated in the peripheral and the center of attention and observers failed to notice the
change (Levin & Simons, 1997). Our current study was conducted to render a greater
understanding of the human need for concentration and attention in order to detect change in an
environment.
Each subject reported to their cognitive psychology lab time to complete the change
detection lab. Upon further discussion with the instructor subjects were instructed to proceed to
cog lab in order to read the experiment debrief. Once comfortable with the instructions students
were asked to complete the experiment during the designated time frame. On half of these trials,
two pictures would be identical. On the other half of the trials, the two pictures differed in some
way. It was up to the subject to determine wither a change occurred while trying to keep a short
response time. The independent variable present in the experiment was wither there was a flicker
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or no flicker. The second variable was if the pictures stayed the same or changed. The two
dependent variables measured were the percentage of correct judgments and the overall response
time. The expected result was that change detection in the non-flicker condition would be
detected with a faster response rate in contrast to the flicker. It was also believed that fewer
errors would occur in the non-flicker condition.
Method
Participants
Forty-one Saint Francis Xavier undergraduate students were asked to complete the
change detection experiment. The 41 male and female students came from a cognitive
psychology class and ranged in age from 18-22.
Apparatus
To complete the experiment subjects were asked to log into a Mac desktop using their
StFX domain name. Once logged in, subjects were instructed to log into CogLab where the
change detection lab could be found.
Method
To begin the experiment, we asked participants to log into their CogLab account and find
the change detection lab located under attention. Avoid using Internet Explore to allow the
program to run smoothly. A total of 16 trials needed completion before terminal data can be
included in the global results. If logged in correctly while on the proper experiment a black box
should appear. Before beginning, only a short period is available to memorize the photo, they
were asked for their best effort. The photo would either flicker or remain idol. The subject was
then asked to decide if a change occurred or not. Once an answer was established two keys were
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designated for the response. If a change did occurred subjects pressed the m-key as quickly as
possible. If no change was noticeable the z-key was pressed. Once selected, the response was
final and the next trial started by pressing the n-key. Once the 16 trials were completed the
option to add the individual results to the global data pool is available.
Results
In the condition with no flicker, participants demonstrated a mean reaction time of
4537.945 milliseconds and a 0.958% correct. For the condition where a grey flicker occurred,
participants demonstrated a mean reaction time of 7860.907 milliseconds and a 0.721% correct.
Figure 1 illustrates the difference between reaction times of the two conditions while figure 2
shows difference in the percentage of correct answers for each condition. Furthering the
investigation of the observed difference between conditions, t-tests were conducted. There was a
considerable difference between the reaction times of the two conditions, t (38) = -6.52, p < .001
along with the proportion correct as well, t (38) = 8.61, p < .001.
Table 1
Means and % correct based on data from 41 participants
_________________________________________________
Proportion Correct
RT (MS)
_________________________________________________
Flicker
0.723
7825.238
No Flicker
0.960
4546.704
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Figure 1. Mean reaction time score based on condition
Figure 2. Percentage correct based on condition
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The original hypothesis was supported based on the data gathered throughout the
experiment. By comparison of the means, it is noted that a faster reaction time occurred in the no
flicker condition in contrast to the flicker. The proportion correct also reflected our original
beliefs resulting in a greater percentage of correct responses in the no flicker condition. By
stating this it’s understood that the flick which occurs has an impact on the overall results.
Trying to depict the change is delayed by the flicker, therefore concentration and attention of the
individual seems to be disrupted, delaying the overall response time.
Individuals may believe that change detection only occurs in an experiment like this. As
stated before, change blindness happens to most people and is when a person fails to detect
change in their surrounding environment. A prime example is when an experimenter initiated a
regular day conversation with a pedestrian. As the conversation grew the initial experimenter
who started the conversation was replaced by his counterpart. One would be led to believe that as
the conversation persisted one would recognize whom they are talking to. Against popular belief
only fifty percent of the pedestrians recognized the change (Simons & Levin, 1998)! How can
this be so? Humans have the ability to recognize tens of thousands of objects in our life time but
individuals could not detect the simple change of the person to whom they were talking to.
Experiments have shown that immediate memory for object identification is very poor (Simons,
1996). This provides us with somewhat of an idea about how this mistake could occur. To
prevent this identification mistake it is advised to associate verbal cues towards the object to
establish easier recognition. This allows us to understand how fifty percent of the individuals did
recognize the experimenter swap.
Knowing this we can have a greater understanding of how the human brain functions.
Aspects such as concentration and attention are extremely important to live a safe life. A great
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example of where this fails to occur is when drivers get behind the wheel impaired. Being
impaired does not allow these drivers the ability to pay one hundred percent attention to the road
and in the end it usually ends fatally.
Knowing that humans struggle to detect change what does this mean for our future. The
world is becoming increasingly technical on a daily basis with the basic understanding that it is
making the daily life easier to live. There are individuals that deal with technology on a daily
basis and without, their job would not exist. What if technology is making jobs increasingly
dangerous with their recent developments? For example, airline commercial pilots are
responsible for themselves but also the lives that reside on their air craft. Change must be
detected and with the knowledge gained throughout this experiment it is understood that we
cannot see it all. When looking at a dash board with over 200 gages help is needed and that is
why auditory detection systems have been put into place. Though, where I see change detection
being most critical is in the military. When looking out over the horizon in Afghanistan it would
be nice to know if activity is occurring thirty kilometers down the road. The technological
advancements in change detection not only allow this to happen but also save lives. In the end,
detecting change is involved in everyone’s life. It is something that we must recognize to survive
because without you might just get hit by a car.
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References
Levin , D. T., & Simons, D. J. (1997). Failure to detect changes to attended objects in motion
pictures. psychonomic Bulletin and Review, (4), 501-506
Levin, D. T., Momen, N., Drivdahl, S. B., & Simons, D. J. (2000). Change blindness blindness:
The metacognitive error of overestimating change-detection ability. Visual Cognition:
Special Issue on Change Detection and Visual Memory, 7, 397-412.
Simons, D. J. (1996). In sight, out of mind: When object representations fail. Psychological
Science, (7), 301-305.
Simons, D. J., & Levin, D. T. (1998). Failure to detect changes to people during a real-world
interaction.Psychonomic Bulletin and Review, (5), 644-649.