RESULTS Human vs Macaques

Transcription

1 14 RESULTS Human vs Macaques As mentioned before, this experiment aimed to test the ability of monkeys in categorizing monkeys and humans into two different conceptual classes. The two classes were presented dichotomously as matching and distractor stimuli. In baseline trials, the photos of matching stimuli were the same to sample stimuli. As expected, in this trials all subjects could associate matching to sample stimuli. They showed high performance of choosing the correct stimuli at the proportion around 90% of the trials. Because the matching stimuli were always of a different category to the distractor stimuli, it might mean they developed different and mutually exclusive concepts of human and monkeys. These results provided a reference to test whether subjects could transfer the newly developed mental concepts to identify new individuals. I did this by changing the matching stimulus with pictures of different humans and different kinds of monkeys. In this test, I found that all subjects associate sample stimuli to new individuals of matching stimuli (Figure 4, Appendix 1, Appendix 4). This same result to baseline (glmmpql, p=0.15; Venables and Ripley 2002) would indicate that the subjects were able to correctly identify new individuals as members of its own class or of human class. This would mean that monkeys categorized humans differently from monkeys. Since the stimuli used in the above experiment contained information on physical properties (that is, shape and color) of the objects, I suggested that the subjects used those properties to create a concept (see Discussion for detailed). I was wondering whether the subjects would still have the ability to identify objects if the informations of the physical properties were reduced. I expected that the subjects will be able to gain informations from the stimuli with a reduced physical properties and combine them with previous concepts they learned before and this would lead them to create higher level of abstraction. For this reason, I deviced three experiments that stripped off certain visual information from the stimuli.

2 15 First, I took color off from the photos and presented it in black and white. I found that the subject's performance in both baseline and test phases were the same (glmmpql, p=0.19) (Figure 5, Appendix 1). This result indicates that even without color, the subjects categorized humans differently from monkeys. In the next step, I tested whether size of the stimuli could affect the performance of the subjects in categorizing humans differently from monkeys. I thought that altering the size of the photos would also perspectively change the shape of the figures. I reduced the size of the stimuli to one quarter of the original and showed it to monkeys. In this case, I tested them using pairs of photos of colored human and M. fascicularis. I found that the subject's performance in both baseline and test phase were the same (glmmpql, p=0.85)(figure 6, Appendix 1, Appendix 4). It means the subjects did not affected by the reduction in size of the stimuli.

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5 18 I continued the test by giving the subjects the blurred and black and white original size photos of human and macaques. These photo manipulations tested whether the subjects could categorize human differently from monkeys though the stimuli lack informations about color and shape. I found that the subjects were able to categorize human separately from monkeys. Their performance in both baseline and test phases were the same (glmmpql, p=0.53) (Figure 7, Appendix 1, Appendix 4). In my last attempt to find out whether the subjects could categorize human differently from macaques, I reduced the size of the black and white, blurred photos of human and monkeys to one quarter of the original size. I found that even in a condition lacking important physical informations, such as color, shape and size, their performance in both baseline and test phases were the same (glmmpql, p=0.57) (Figure 8, Appendix 1, Appendix 4). It means that the subjects could categorize human differently from monkeys. Overall, by seeing the high performance of the subjects when tested by the manipulated stimuli, I concluded that they were able to develop higher level of abstraction based on available concepts they have learned before. Macaca fascicularis vs other macaques This experiment aimed to test the ability of monkeys in categorizing M. fascicularis differently from other macaque species. In this experiment I used two paradigms, that is, M. fascicularis vs M.mulatta and M. fascicularis vs M. fuscata. In baseline trials of both paradigms, the photos of matching stimuli were the same to sample stimuli. Thus, all subjects could associate matching to sample stimuli at around 90% of trials. Similar with human vs macaques experiment, the matching stimuli were always of a different category to the distractor stimuli, so this result might mean they developed different and mutually exclusive concepts between M. fascicularis and the other macaques; that is M. mulatta and M. fuscata. This result provided a reference to test whether the subjects could use the developed concepts of M. mulatta to identify new individuals of the species; the same also true for M. fuscata. I did this by changing the matching stimulus with pictures of

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7 20 different individual of monkeys. I found that all subjects associate sample stimulus to new individuals of matching stimuli (Figure 9, Appendix 2, Appendix 4). This same result to baseline (glmmpql, p=1) indicate that the subjects were able to correctly identify new individuals as members of their respective class. This would mean that the subjects categorized M. fascicularis differently from the two other macaque species. As in the first experiment, I ascertained this categorization ability by taking color off the photos used in the stimuli and presented it in black and white color. I found that all subjects associate sample stimulus to black and white version of the matching stimuli (Figure 10, Appendix 2, Appendix 4). This same result to baseline (glmmpql, p=1) would indicate that even without color, the subjects could also categorize M. fascicularis differently from other macaques. Human vs Non-Human This experiment aimed to test ability of monkeys in categorizing human differently from non-primate animals. In this experiment, I used several photos of human and non-primate animals, such as mammals, birds and reptiles and amphibians. I tested the subjects using both color and black and white photos. For baseline trials, I used same photos of human and M. fascicularis that used in baseline trials of Human vs Macaques experiment. I found that the subjects did high performance in test trials, similar to that in baseline trials (glmmpql, p=0.65 for colored stimuli and p=0.70 for black and white stimuli) (Figure 11, Appendix 3, Appendix 4). It means that they were able to maintain concept of human and developed new concept about non-human.

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9 22 DISCUSSION Fujita and his coworkers (1993, 1995, 1997) found that monkeys see their conspecific longer compared to other species, and this were thought to lead to species discrimination. His works using various kinds of pictures of macaques give us an insight into how monkey learn to categorize via species discrimination. However, the methods that he used could be doubted; for example, there were several interpretation for how monkeys see conspecific in longer duration. First, the longer reaction time might mean that monkey's attention varied in response to different pictures regardless of their species membership. Second, they were mostly wild born so they have already familiar with their own species since opportunities to learn facial properties of members of its own species exist in the life history of the monkeys. Thus, monkeys may prefer to look longer at a picture that is similar to their group mate and, by doing so, exclude pictures of another species. Although it can be considered as species discrimination, it's still not clear if monkeys can discriminate various species excluding their own. Third, since most experiments (Demaria and Thierry 1988, Fujita 1993, Fujita and Watanabe 1995, Fujita et al. 1997) did not control features, such as backgrounds, of the stimulus, it is hard to conclude which part of the stimulus attracts the monkeys attention. The method of matching to sample task I used might be more reliable than counting perceptual duration for several reasons. The task of associating matching and sample solves the first and second problems of Fujita (see experiments on M. fascicularis vs non M. fascicularis below). More over, by controlling the background of stimuli, and the use of a specific body part (that is, face), I tried to reduce information noise which may distract my deduction. Thus, since my stimuli represent real objects (Dasser 1987, Kyes et al. 1982), this experiment showed that monkey could discriminate species. Therefore, my method should make a strong conclusion about the ability of categorization in M. fascicularis. The first experiment to show the ability of categorization in M. fascicularis was the discrimination of human vs monkey. In the training phase, I

10 23 introduced pictures of human and monkey to the subjects. There were consistent similarities and differences of physical properties between human and monkey pictures. It is not unreasonable to conclude that the subjects used these similarities and differences to create a conceptualized mental image of human that differs to that of monkey. There are some physical properties that provide information to create concepts. First is shape. The global and local shapes of human's and monkey's faces are very different. While human faces are oval, monkey's faces are rounded with hair on it. Another possibility is that the subjects detected the presence of the eye. This mechanism, called eye direction detector, is important to understand facial emotion (Farroni et al. 2002, Baron-Cohen et al. 1999). Given the eyes, its angles with nose and lips of both species are different. The second is color. In this experiment, I used colored photographs. As seen in stimulus photos (Figure 2), compared to uniformly presented background color, the global color of the monkeys was different to that of human. Indeed, this had been shown by Santos (2001) that colors are used as information to categorize object. Those informations may help the subjects to recognize and discriminate between categorically human and monkey. The resulting concepts of human and monkey learned from training phase were used by M. fascicularis individuals as basis to categorize pictures in the test phase. In every trial of test phase I changed the baseline pictures with new ones. This would prove the ability of the subjects to transfer its concepts to respond to novel stimuli. For the monkey pictures, I used three different species of macaques. I found that proceeding from baseline to test trials performance of the subjects remained the same. These indicate that the subjects categorized monkey as monkey and human as human. It is interesting to note that although two of the subjects (Ucok and Sukhoi) had never saw other species (M. fuscata and M. mulatta) for their entire life, they categorize photos of those species as monkey instead of human which in captivity they see everyday. It might be concluded that they had concepts of human and monkey based on different color and shape of the stimuli. I may interpret this fact as the monkeys recognized natural discontinuity between the two class; Rosch et al called this as basic level of abstraction.

11 24 As this kind of categorization ability was based on perceptual similarity of physical attributes of the photos discussed above I may also describe this as the concrete level of abstraction (Vonk and MacDonald 2002). In nature, sometimes there are conditions (such as at long distance or less light conditions) where monkeys could not see detailed information of object to do categorization. Thus, they have to be able to categorize objects based on broad, generalized concept that is developed on concept with complete and detailed physical percepts. According to Rosch et al. (1976), the world is structured because real-world properties do not occur independently of each other. Because of this correlation, few properties of an object would suffice to predict the whole properties. After seeing the results of the above test (which were positive), I wondered whether the subjects would still have the ability to identify objects if the informations on the physical properties of the stimuli were reduced. This would simulate natural conditions and further proof the ability to transfer the learned concept in my subjects. I then manipulated the stimuli by taking color off the matching and distractor stimuli. The result showed that the ability of all of the subjects to categorize between human and monkey was not hampered. They could successfully transferred their mental image to the black and white photos. This fact showed that the subjects did not depend on color and use other informations to discriminate the stimuli. Some studies showed that monkey may use global shape (Dittrich 1994) and local features (Demaria and Thierry 1988) of object as informations in categorizing object. Jitsumori and Matsuzawa (1991) showed that M. mulatta and M. cyclopsis were able to classify human shilouettes as human and assume that monkeys used global shape to recognize human. Rosch et al. (1976) explained that levels of abstraction are nested. At the basic level, objects within category shared most similarity in concrete properties. When it goes to the more abstract levels, it share less properties among each other. Thus, we may follow that the use of global shape is one way monkey used to generalize the physical properties of an object. To test whether the subjects might be able to generalize their physical percepts, I blurred or resized the stimuli to reduce and/or to change the local shape informations carried by the stimuli. Again, in all of these extended

12 25 tests, the M. fascicularis subjects showed high performance of discrimination. This ability to classify blurred or resized photos of human as human and blurred or resized photos of monkey as monkey demonstrated that the subjects were looking for features of blurred or resized matching stimulus that have common properties with those of sample stimulus. It seemed that the subjects subtracted the local shape differences to get a generalized concept of object. Compared to basic level of abstraction proofed before, this generalized level of abstraction showed that the subjects performs at least two levels of categorization by learning from their experience in training and test phases. For second experiment, I tested the ability of M. fascicularis in discriminating M. fuscata or M. mulatta against their conspecific. Those macaques belong to fascicularis group (Fooden 1969) so they shared many similar physical properties of face, such as the existence of facial hair and other local shapes. Thus, the monkeys have to extract the differences from total facial properties to get the uniqueness of each species. Result of the experiment showed that monkeys could discriminate their conspecific from other species. They may used color as information, since the hair color of M. fascicularis in the stimuli were lighter than that of M. mulatta and darker from M. fuscata. More over, the facial color of M. fascicularis is relatively brownish while M. mulatta paler and M. fuscata reddish. In Human vs Macaques experiments, when color information was discarded, the monkeys used (whether global or local) shape informations to categorize the two different classes. Thus, I took the color off the stimuli and found that the subjects again showed high performance of discriminations. This adds to my conclusion that the subjects were able to detect the differences in physical properties of each species and use it as basis in discrimination. This experiment showed the categorization ability the other way around from the first experiment; that is, the transfer of concept from general to specific. The Human vs Macaques and M. fascicularis vs Other Macaques experiments showed that M. fascicularis were able to develop concept using informations from similarity and difference of physical properties to put objects into one particular class. However, in some conditions, it takes more than physical

13 26 similarity to put objects into one group. One object may relate to others based on relations that could not be detected easily by sensory properties. Thus, in this case, the subjects need the ability to associate different conceptualized mental images to discriminate stimuli lacking in physical clues. The class that is created does not rely on perceivable features and may reflect a more conceptual understanding of category belongingness. This kind of concept assisted higher level of categorization. To test whether M. fascicularis were able to create such a more abstract concept, I did Human vs Non-Human experiment. In two previous experiments, there are physical similarities between all sample and matching stimuli. In Human vs Non-Human experiment, I dismissed physical similarities within one category; that is, Non-Human class consisted of photos of animals such as mammal, bird, reptile and amphibian which were different in many ways. At first I tested them with colored stimuli. Our subjects showed high performance in discriminating between human and non-human classes. Since there are no similarity within non-human category, I may suspect that the subjects use color information to do categorization. Still, if I took color off the stimuli, the subjects discriminated non-human from human. I assumed that the monkeys created a new concept, that is concept of non-human that differ from concept of human. Thus, the result clearly showed that the subjects could perform higher level of abstraction.