Medieval ideas about cognitive psychology derive from two major sources, the writings of Aristotle and especially his work on the soul, the De Anima, and the theory of the inner senses, which was laid down in late antiquity. Aristotle’s De Anima may be the most popular psychological text of all time: It was prescribed reading for Bachelor of Arts degrees throughout Europe until the end of the Middle Ages. The book is short and at times obscure, but it offers a systematic account of psychology with Aristotle’s ideas about other disciplines. Because of its obscurity, a number of medieval scholars wrote books or commentaries in which they set out what they thought Aristotle meant. Those by Averroes and Aquinas are probably the best known.
In the De Anima, Aristotle defined the soul as what the body is for. He differentiated the types of soul possessed by plants, animals, and humans by the different faculties they possess. Plants are capable of nutrition and reproduction. Animals have the additional faculties of appetite (which includes motivation), sensation, and locomotion. Some animals are capable of three cognitive processes: common sense, which sums up and differentiates the outputs of the five senses; imagination, the power to summon up images of objects previously seen; and memory. In Aristotle’s psychology these faculties are believed to operate in physical organs. Humans have all the animal faculties plus those of reason and will, which are not apparently housed in physical organs.
Both the Islamic and the later Christian scholars seem to have set themselves the task of fleshing out this theory. This task was helped by a medical account developed around the fourth century CE, sometimes known as the theory of the inner senses, which postulated that the cognitive processes of the common sense, imagination, and memory were performed in the ventricles of the brain.
In Avicenna’s version of the theory, there are three ventricles arranged linearly in the head, all filled with a fluid or spirit. Sensory information is sent to the front ventricle, which has connections to the middle ventricle, which in turn, connects to the rear ventricle. (The assumed anatomy differs markedly from the present-day account.)
In perception, the common sense, located at the front of the front ventricle, receives images (or forms) of objects in the world from the individual senses. At the back of the front ventricle is an image-store, which was supposed to have a waxy consistency that could retain these images indefinitely. The process of imagination involved displaying this stored form once again to the common sense.
Two processes that Avicenna thought took place in the middle ventricle extracted meaning from the images: cogitation put together or subtracted components of the images that had been previously perceived (this is how one can imagine a golden mountain. to take a medieval example); estimation abstracted implications or meanings from the images either instinctively or as the result of past experience. So, to take two of Avicenna’s examples, the sheep instinctively fears the wolf, and the dog cringes in terror from the stick it has been beaten with before. Finally, the rear ventricle contained the memory, which stored the associations and meanings obtained from estimation.
The cognitive processes of animals could be completely explained by these operations. However, Avicenna believed that humans also had an immortal, rational soul or mind that had no physical organ at all. Avicenna suggested that the inner senses processed information about individual objects or events, whereas the mind processed more abstract, universal information. Also, in the normal waking person, the inner senses were under the control of the mind.
There was some debate about the details of the inner senses theory, but the basic paradigm was unchallenged from the fourth to the sixteenth century, and it is referred to by medieval physicians, philosophers, theologians, and even poets. Debate about the activities of the mind, which were only described in brief outline by Aristotle, was more intense, partly because religious issues were often involved. Medieval scholars questioned, for example, whether universals (like the concept of “cat”) existed only in the mind or had some external reality; whether minds were individual or whether there was one collective mind in which all humans participated; how intellectual concepts might be stored; and how necessary the processes of the inner senses were for thinking.
Splitting cognitive functions between the inner senses and the immortal mind gave rise to theological problems. For example, if your memory for your individual actions is in the inner senses and perishes when you die, how can you know after your death what good or bad things you did when alive, and which earned you heaven or hell? But this disadvantage was offset by the range of phenomena that could be explained by the combined processes.
Dreaming and hallucination, for example, were easy to deal with. In the normal, waking person, imagination and cogitation are under the control of the mind, but when people are asleep or deranged, the images in the image-store are spontaneously retrieved and perceived. The inner senses were thought to include two memory stores (the image-store and the memory), and often the mind itself was thought to have a store for intellectual concepts or intellectual procedures such as the rules for speaking a foreign language. This partitioning of memory could be used to explain a range of phenomena. For example, Avicenna suggested that memories could be reconstructed if information had been lost from, say, the memory, but not from the image-store. Aquinas thought that the tip-of-the-tongue phenomenon arose when there were references stored in the mind, but the particular information stored in the inner senses could not be immediately accessed.