MIMS Technical Report No.00045 (201409221)

A preliminary report:

Do hunter-gatherers have illusions?

Joe Yuichiro Wakano*1, Kokochi Sugihara*, Hideaki Terashima2, Taro Yamauchi3*Meiji Institute for Advanced Study of Mathematical Sciences, Meiji University
1<joe@meiji.ac.jp>
2Faculty of Humanities and Sciences, Kobe Gakuin University
3Graduate School of Health Sciences, Hokkaido University

Abstract
This is a preliminary report that studies whether modern hunter-gatherers have illusions,i.e., erroneous perceptions of reality occurring when they watch intentionally designed movies.
Experiments were performed in southeast Cameroon and Baka Pygmy hunter-gatherers
participated. The result suggests that hunter-gatherers do have illusion.

1. Introduction
Illusions occur when a human sees a 2D image and converts it to a 3D image in brain.
Since the conversion from 2D to 3D is mathematically an ambiguous task and since infinite
solutions could exist, human brain has to assume some prerequisites in the conversion process.
Many examples of illusion exploit human tendency to assume regular patterns such as parallellines and squares (the angle of 90 degrees). An interesting question is whether this tendency is
genetically determined or culturally acquired after birth. If the tendency is culturally acquired,modern human are more likely to see illusion since they grow and live surrounded by modern
architectures which are full of geometrically regular patterns such as parallel lines and squares.
There is a possibility that individuals living in an environment where few geometrically regularpatterns exist have weaker or no tendency to have illusions (i.e., be hallucinated) than individuals
living in modern cities. To test this hypothesis, we perform experiments with hunter-gatherers inCameroon.
12. Method
2.1 Participants
The participants of the present research are hunter-gatherers children and adults in avillage Payo near the village center of Lomie, southeast Cameroon. The tribe belongs to BakaPygmy. The Baka are a group of African Pygmy hunter-gatherers that live in the African rainforest
extending over Cameroon, Gabon, the Central African Republic (CAR) and the Republic of Congo.
The participants speak the Baka language and some of them speak French. None of them speak
English. The experimenter (the first author) knows neither Baka nor French, and thus there was no
linguistic communication between the experimenter and participants.
Although many neighboring villages are 'modernized' in a sense that their primaryoccupation is agriculture (farmers) and they frequently exchange goods in a market, most Baka
Pygmy tribes have kept their traditional culture of 'hunting-and-gathering'. For this area, it is said
that cultural and genetic hybridization between hunter-gatherers and farmers is far less than theexpectation from random communication/mating model (i.e., quite rare).
Following the Cameroon government's policy and the rapid development of rural areas,
Baka Pygmy tribes are also being 'modernized', and thus the importance of the present observation(as of 2014) should be noted.
The physical and cultural data of participants (e.g., age, sex, health state, education) were
not taken in this preliminary study. They happened to be there on 8th August 2014 at the location(3°8.734 N,13°42.471 E).

The location data was taken by GPS function of a smart-phone (NTTdocomo SC-02F).
Children, whose ages are estimated as from 3 to 15 years old, joined the first experiment.
All the children looked healthy and this group consists of both boys and girls. Three adult males
joined the second experiment. They also looked healthy. They are from families ('Ie' in Baka) of
Nboku, Monbito, and Makunbo. Their level of education was not studied, but the environment
suggests that they have never seen modern architectures such sky-scrapers.

2.2 Illusion movies
We prepared 3 illusion movies (I1, I2, I3), each of which lasts for 1 minute. For control, wealso prepared 3 movies (N1, N2, N3) which look the same in the beginning but no illusion occurs. Intotal, we prepared 6 movies.
Examples of snapshots of the movies are shown in Figs. M1 and M2. Fig. M1 shows threescenes of the first illusion movie I1. As shown in Fig. M1(a), there is a solid having two windows,
and a straight red rod appears. Then, as shown in Fig. M1(b), the red rod is inserted through thetwo windows simultaneously, which looks impossible. Finally, as shown in Fig. M1(c), the solid
together with the rod is rotated so that we can understand the true shape of the solid. In the2corresponding non-illusion movie N1, the initial scene is almost the same as Fig. M1(a), but the rod
is inserted through only one window, and the scene is rotated, by which we understand that theshape of the solid is the same as we perceive in the initial scene and hence no surprise.

Fig. M1(a)Fig. M1(b)Fig. M1(c)3Snapshots of the third illusion movie I3 is shown in Fig. M2. Initially, as shown in Fig.
M2(a), there is a solid having four slopes. Next, as shown in Fig. M2(b), wooden balls put on theslopes look as if they are rolling uphill toward the highest center. Finally, the scene is rotated asshown in Fig. M2(c), by which we understand that the center is the lowest, and hence the motion of
the balls is consistent with the gravity. In the corresponding non-illusion movie N3, the initial sceneis the same as Fig. M2(a), but when the balls are put on the slopes, they roll downhill, and when thescene is rotated, we understand that the initially perceived shape of the solid is correct.

Fig. M2(a)Fig. M2(b)Fig. M2(c)4Movie files were played with a tablet (Google Nexus 7). Files were saved in Japanese file names toprevent a participant to read the content.

2.3 Experiments
Participation to the experiments was completely spontaneous. No instruction was given byexperimenters. Upon the arrival to the village (the arrival of the research group had beenannounced) and after exchanging greetings, we put a tablet on the ground. It seems that theimpression "something fun will begin" has attracted most child participants.
Movie files were shown in the following order; N1, I1, N2, I2, N3, I3. No word was spoken
by an experimenter.
The experiments were performed twice (child group and adult group in this order in thesame day and at the same village).

3. Results
3.1 Child group
Since there is no scientifically-accepted way to detect whether participants have illusions,
we took photographs during the experiments. After a sequence (N1 - I3), the same sequence isrepeated. After several sequences, participants lost interests in normal movies (N1, N2, N3) while
they still showed interests in illusion movies (I1, I2, I3). There was variation in their attitude; some5participants looked concentrating on all the movies, some were interested only in the illusion
movies and some lost interests in all the movies after the first sequence. Examples of faces ofchildren looking at an illusion movie are shown below.

3.2 Adult group
The same sequence was displayed. They showed more interests in illusion movies (I1, I2,6I3) than normal movies (N1, N2, N3). After two sequences, they talked with each other. It seemedthat they had particular interest in a rotating scene in a movie file I2, which is intended to showthat the initially perceived 3D structure is different from the true 3D structure, and hence mighttell why illusion occurs. The experimenter repeated this part. Examples of faces looking at anillusion movie are shown below.

74. Discussion
In summary, this preliminary study suggests that hunter-gatherers do have illusions. Thus,by this study, the origin of illusion cannot be attributed to culture or environment.
Several points need to be discussed. Firstly, the occurrence of illusion is judged mainly by
the experimenter (the first author). Only photographs describe what actually happened during ourexperiments.
Secondly, we need to take into consideration that the participants were already in a processof 'modernization'. They lived in farmer's style houses which are square shaped, while theirtraditional house is round-shaped (shown below). A possible reason for them to have illusion is thatparallel lines and squares exist in their life because of recent 'modernization'.

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We speculate that the effect of recent 'modernization' had little effect on our result. Alreadyin their traditional house, there is a supporting structure which is perpendicular to the ground (astick supporting the round roof, see the photograph above). They also make bows and arrows tohunt games. To understand how bows and arrows work, they must have principal ideas in physics
and geometry. Thus, even if parallel lines or squares are less seen in hunter-gatherers' life, it isquite natural that they know parallel lines and squares. How brain works to make illusion isanother problem, but the followings are not contradicting:1) Hunter-gatherers live in an environment with few geometrically regular structures.
2) Hunter-gatherers do have illusion based on such geometrically regular structures.

Acknowledgments
This work was supported in part by Monbukagakusho grant 22101004 to JYW. The authors would
like to express gratitude to all Baka people that participated in our study.

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