(Paper compiled from individual papers written by the seven student in PSY 440, Spring 2000)
Return to PSY 440 frontpage, Spring 2000.
The influence of the human brain on visual perception is largely studied in the field of psychology today. Understanding the way memories, experiences and expectations are perceived can enhance the way we view perception as a whole through better understanding. One way of studying the way that memory and experience interact with perception is to look at the differences in true object perception and perceptions influenced by memory and experience. Perceptions influenced by the visual field itself, or changes in stimuli are referred to as "bottom-up" influences. If a perception is influenced by what a person expects, or has experienced before, it is referred to as "top-down" influence. One way to measure the differences in these two types of processing is to present a stimulus to people that can be perceived in more than one way. Ambiguous figures are stimuli that contain two perceivable images that seem to reverse. Only one image in the reversible figure can be perceived at one time, allowing researchers to examine a recordable response from participants (Stark, 1999). The idea of this separation of images is commonly referred to as "figure-ground reversal", and was a major influence of Gestalt psychologists. One of the most famous examples of this type of figure is the "face-vase" figure introduced by Danish psychologist Edgar Rubin in 1915 (Goldstein, 1999). Using this type of stimulus, researchers can manipulate both the expectations of the participant prior to viewing the figure, or the actual physical characteristics of the figure itself, biasing recognition of one image over the other.
The term top-down processing refers to the expectations, memories, biases and general upper-level influence the brain has on perception. If a person views an ambiguous figure and is predisposed to see one figure instead of the other, then this top-down predisposition can affect the way he sees the image. This influence has been shown to be quite strong. For example, Thomas (1999) demonstrated that participants who were shown a reversible figure briefly, and then were asked to sketch the figure they perceived, could not identify the other figure from their sketch. After drawing the image they initially perceived, participants were even told what the other image was, and still could not identify it in their sketch, even though the drawings were not very dissimilar from the original. This gives us an idea of how strong the top-down influence on visual processing can be.
Another example of this influence can be seen in a study that demonstrated the effect of logical motion on these figure identifications (McBeath, Morikawa, and Kaiser, 1992). Participants were shown reversible figures in which both figures could be associated with motion. When the image was shown while moving in a particular direction, participants were more likely to identify the figure that would logically move in that direction. For instance, if the figures in the image were two animals, participants would be more likely to recognize the animal facing the direction of motion. Bernstein and Cooper (1997)further demonstrated this effect in a study showing the same bias when reversible figures were moved in a logical direction. Both of these studies show a strong influence of top-down processing on figure recognition. The importance of top-down processing on figure recognition was further supported in a report by Long and Toppino (1994). In their report, they simply compiled the results of several studies and explained how the data supported the importance of top-down processing on visual perception.
The role of bottom-up processing can also have a strong effect on what people perceive. The stimulus itself can be altered in such a way that it is more likely to be seen as one figure than another. Even though both objects can be recognized, perception of one can be strengthened through altering its characteristics. One example of this is the ideas presented on an Internet site from the Illusionworks Company. The Internet site points out that when viewing these reversible figures, focusing on one particular segment of the figure can cause the viewer to be biased towards seeing one image instead of the other. If the focused area is more similar to a characteristic in only one of the objects, they will most likely see that particular object (Illusion Works, L.L.C., 1997).
Long and Olszweski (1999) conducted two experiments to examine bottom-up processing in the reversibility of reversible figures. They hypothesized that numerous stimulus and procedural variables can be expected to interact effectively in any research effort, given the combined roles of both sensory and cognitive processes in phenomenal reversals. Stimulus control was found to be critically important in this experiment. The size of the stimulus, stimulus location, viewing duration, fixation control, and other bottom-up variables affected the number of reported reversals in this experiment. Although the purpose of their experiment was to examine the influence of bottom-up processing on reversible figures, the researchers noted that the observers' prior experience with the figures, their expectations in the setting, their attention, and other top-down variables may have also influenced the reported reversals. This study was further reinforced when analyzed by Peterson (1999). He agreed that both bottom-up and top-down processing influence perception.
The literature reviewed for this study demonstrates that a person's perception of an ambiguous figure can be influenced in several ways. Through manipulating either the stimulus itself, or the participant's expectation of what they will see, we can expect a greater likelihood of the emphasized figure to be recognized first. In the current study, the roles of top-down and bottom-up processing on visual perception were examined. The question addressed was the degree to which we can influence visual perception, through manipulations of the visual field or of the expectations and experience held in memory.
It was hypothesized that the presentation of bottom-up cues added to an ambiguous figure would be more influential than the presentation of top-down cues presented before an ambiguous figure. This hypothesis was derived from the idea that the early, or first, visual processes behave mostly in a bottom-up fashion, separate from cognitive or top-down processes (Illusion Works, L.L.C., 1997). It was also hypothesized that the gender of the participant would affect the influence of the priming and perception of the figure.
Method
Participants
Eighty-four, 42 male and 42 female, students enrolled at Stephen F. Austin State University were asked to participate in this study. The majority of the participants were age eighteen through twenty-five. Participants were individually solicited by the seven members of the research group, and received no compensation. Participants had 20/20 or corrected to 20/20 vision and had normal color vision. Participants were treated in accordance with the "Ethical Principles of Psychologists and Code of Conduct" (American Psychological Association, 1992).
Design
A simple, mixed design was used, with the independent variable (prime type) having seven levels (label, word scenario, picture scenario, neutral, color, detail, and lightness/ contour), and the dependent variable (participant response) having one level. Gender was also included as an independent variable.
Materials
There were seven different reversible figures that were manipulated in seven different ways (prime type) for each of the two interpretations of each reversible figure. Thus, there were 49 figure manipulations, times two. The three top-down prime type conditions consisted of a prime sheet containing a label, a word-scenario, or a picture. The three bottom-up manipulations consisted of a color addition to the ambiguous figure, added detail, or a change in the lightness contour. For example, the ambiguos figure presented in Figure 1 can be identified as either a man playing the saxophone or a woman's face.
Figure 1
For the label priming of this figure, the phrase "saxophone player" appeared on the prime sheet to influence the perception of the saxophone player, or the word "woman" appeared for priming of the woman. For the word-scenario conditions, the descriptions were of a jazz club or a woman's role in a film. The last top-down influence was the picture scenario, which consisted of a picture of a trumpet or a picture of three women. Color manipulations included a gold colored saxophone for the priming of the saxophone player, and pink colored lips in order to prime the woman's face. The detail manipulation consisted of the appearance of musical notes at the end of the saxophone or chin continuation and eyelashes on the woman. The last bottom-up influence consisted of manipulation of the color contrast of the figure in which the saxophone player appeared lighter, or the woman's hair appeared darker. The packet also consisted of one neutral ambiguous figure that was not exposed to any type of priming.
In order to prevent a participant from viewing an ambiguous figure more than once, each of the seven experimenters had a two-part packet containing consent and debriefing forms, and seven different reversible figures that were manipulated in seven different ways. The two parts separated the two interpretations of the ambiguous figures. For example, one part would have the color prime for the saxophone interpretation and the other would include the color prime for the woman's face interpretation. Thus, each participant would be exposed to all seven ambiguous figures, and all seven prime types, but would not see any of them more than once. The order of presentation of the seven levels of prime type were partially counterbalanced across the experimenters and was then fixed for each packet.
Procedure
The seven experimenters each solicited 12 volunteers to participate in the experiment, three males and three females for both parts of their packet of stimuli. Before receiving the consent form, the experimenter explained to the participants that participation was voluntary and could be terminated upon their decision at any time. All participants were tested individually in a comfortable pace. Participants were given approximately 30 seconds to examine the condition relevant to the ambiguous figure that was presented. Following presentation of each condition, the participants were asked what figure they perceived first, and this was recorded. After completion of the packet, the debriefing form was given to the participants.
Following the collection of data, each of the subjects' responses were changed to a "yes" if the subject saw what was primed, and to a "no" if the subject did not see what was primed.
Results
The results were first compiled into a table. Women's responses were separated from the men's, and rows were made up of each possible figure, totaling fourteen rows per gender. Columns were made up of the type of prime used, totaling six columns. A final column in which the unaltered data were recorded was added for comparison, but was not used in the analyses.
Responses were recorded using percentages. For example, for the devil word prime, one out of three women saw the primed "devil", therefore, a percentage of 33 was recorded on the table. The data were then analyzed using a two-factor mixed design ANOVA. The between factor was gender, and the type of prime that was presented was the within factor.
The effect of gender was not statistically significant, F (1, 26) = .91, p > .05. However, a significant effect for prime type was revealed, F (5, 130) = 3.94, p < .01. A Post Hoc Tukey HSD was performed on prime type and revealed significance pertaining to the type of manipulation presented. The detail manipulation of the ambiguous figure was significantly more influential than any of the top-down manipulations. The color and contour manipulations were not significantly more influential than the top-down manipulations.
Although there were no significant results pertaining to the gender variable nor a significant interaction between prime type and gender, females tended to be influenced more strongly by the primes than males. Specifically, the biggest difference between males and females occurred using the picture prime. The graph presented in Figure 2 represents the means of the male and female percentages of responses matching the prime type presented.
Figure 2:
Finally, when prime type was collapsed to two levels (Bottom-up v. Top-down), and the ANOVA was repeated, there was a significant difference between the two types of priming, with bottom-up priming being more influential than top-down priming, F(1,26) = 7.51, p<.01.
Discussion
This research was an attempt to determine whether the presentation of top-down cues presented before an ambiguous figure, and the presentation of bottom-up cues added to the figure, would influence an individual's first perception of the figure. The topic of whether the gender of the person being primed influenced the perception of the figure was also addressed.
Tuccio (1995) stated that there are many stimulus conditions and factors that influence an ambiguous figure's perceptual organization. Manipulating ambiguous figures by using a word label, word scenario, or picture scenario prime sheet for top-down cues, and adding color, detail, or changing the color contour for bottom-up cues was the method used in this research in order to provide each participant with the six different prime types. The Two-Factor, Mixed ANOVAs that were used in this study revealed a significant difference between the influence of top-down cues and bottom-up cues. In general, the presentation of bottom-up cues was significantly more influential than the presentation of top-down cues. More specifically, the bottom-up manipulation that consisted of adding detail to the ambiguous figure appeared to influence the participant more than any of the top-down cues. These results may suggest that what an individual ultimately perceives is based on certain aspects of the stimulus, such as its color, any detail that it contains, and the color contour of the object. This conclusion corresponds to the conclusions drawn by Cave and Kim (1999) which revealed that a color distractor, a bottom-up cue, could draw attention to a stimulus in the early stages of visual processing. A second possible explanation for these results is that adding detail to a picture simply allows a person to recognize it more effectively than color or shading, and our experiences and memories, while influencing us somewhat, cannot compete with a real stimulus in the environment.
According to the results addressing the hypothesis that gender affects the influence of priming of an ambiguous figure, overall there was not a significant difference between males and females in their responses. However, when looking at the means of the responses, females tended to be influenced more strongly by the top-down primes than males. The biggest difference of influence occurred in the prime using the picture scenario.
An additional suggestion that there may be gender differences even though the above results were insignificant comes from an examination of the actual responses when subjects were reporting what image they first perceived in the reversible figure. More specifically, for some reversible figures, the male participants tended to see different interpretations than those determined by the experimenters (who were predominantly female). For instance, with an ambiguous figure that could be seen as either "arrows" or the word "win" some of the male participants identified the arrows as "soldiers". Thus, more males might have matched the primed interpretation if the word or scenarios chosen had been congruent with the "soldier" interpretation rather than the "arrow" interpretation.
In summary, both top-down and bottom-up processing appear to have a complicated effect on the way we perceive the world. The details present in an object seem to be very important to our recognition of that object, and females may be more flexible in their perceptions of the world, allowing experience and stimulus characteristics to play a larger role in object recognition. This study has not definitively answered the questions it sought out to, but has perhaps raised a few questions in the minds of future researchers. The effects hinted at in the results of this study should be pursued on a broader level, using many more participants as well as many more reversible figures to obtain a better, clearer picture of the effects of our memories, experiences, and the details of the environment on visual perception.
References
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Illusionworks, L. L. C. (1997). Perceptual ambiguity. http://www.illusionworks.com/html/perceptual_ambiguity.html
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