Quoted from Genshiken:

In reply to:

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"[...]human beings use their imagination when viewing things, and even see these abstract symbols as something else. Could you say that this is a basic function of the human brain. [...] In other words, people who claim they "can't get off on cartoons" suffer from a defect in their brains... Or else they're just showing off!!"

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The full scene includes examples from crude drawings and carvings from ancient times (i.e. the "godesses of fertility").

Edit:
animated gif with the sequence. win:




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