Kyzikos is a fitting polis with which to conclude this book because its coinage and two extant lead weights provide unparalleled insights into one major subject city’s relationship with Athens that we would not otherwise know about in such detail. Their coinage and the weights advertize, uniquely, as far as we know, a close relationship with Athens.

Athens’ and Sparta’s respective worlds changed radically in the winter of 413. The Athenians’ attempt to conquer Syracuse, and with that, as noted in the previous chapter, the expedition was shortly to end in catastrophe, especially when a Spartan detachment to Sicily to help the Syracusans proved pivotal in the war. Also in 413 the Spartans installed a permanent fort at Dekeleia in northern Attica. This directly threatened the mining industry at Laureion, but instead of withdrawing from the Sicilian campaign in order to face the new threats at home, the Athenians pressed on when reinforcements arrived from Athens. (We noted in Thucydides’ mention of the eikoste [p. 107], his gripping account of the Athenians’ determination to proceed now with two wars.) In Sicily, however, the Athenians met with utter defeat.

Conditioning affects a wide range of behaviors, far beyond just salivation. One is how we react to painful stimuli. Our bodies work to maintain internal states within safe limits (homeostasis), and conditioning allows us to anticipate painful stimuli, and to take action to counteract them. Conditioning also affects a wide range of emotions, including fear, hunger, sexual arousal, and cravings for alcohol and drugs. And conditioning can also be used to treat problems involving these emotions. In aversion therapy, exposure to alcohol is followed by inducd illness; by creating an aversion to alcohol, this therapy has had considerable success in treating alcoholism. Conditioning has also been used to treat phobias. Phobias often develop through conditioning, and conditioning principles can be used to overcome them. In exposure therapies such as systematic desensitization, the feared stimulus is presented and not followed by harmful consequences (in one variant, virtual reality therapy, the stimuli are presented through virtual reality headsets). The aim is to extinguish the fear, and this treatment too has had considerable success.

One assumption underlying research on learning and memory is that behavior is lawful, determined by our environment and heredity. Examples of powerful influence include child abuse, aggression, advertising, and sexual attraction. These examples reveal how powerfully our behavior can be determined, sometimes without our knowledge, but they do not rule out the possiblity that we also possess some free will. A second assumption is that the best way to discover laws is through experiments. Experiments allow us to separate possible causes of behavior, but finding appropriate control groups can be tricky, slowing progress. Two contrasting approaches have dominated psychology, influencing what topics researchers choose to study: behaviorism and cognitive psychology. A third assumption is that studying animals can be helpful in analyzing behavior, because animal research allows greater control of environmental and genetic variables, and animal and human behavior is far more similar than once believed—as shown, for example, in the ability of chimpanzees and even birds to acquire English vocabulary. However, animal research can also raise difficult ethical issues. The chapter concludes with an introduction to some of the key forms of learning and memory that will be discussed.

To study memory, Ebbinghaus memorized lists of nonsense syllables. He found that success depended on the amount and spacing of trials, and that forgetting occured rapidly at first but then more slowly. He believed that practice strengthens associations, but research on levels of processing showed that practice is not sufficient; deeper and more elaborate processing enhances memory. Similarly, research on textual material demonstrated that we don’t just associate successive words; we abstract and store their underlying meaning. Purely associative accounts also proved unable to explain the acquisition of motor skills; we create motor programs to guide our movements. To understand all these processes, psychologists adopted an information-processing framework, studying how information is coded, stored, and retrieved. Important clues came from two discoveries: that participants can remember only about seven new items at one time, and that these items are forgotten within seconds if rehearsal is prevented. To explain this, Atkinson and Shiffrin proposed that information is initially held in a temporary or short-term store that has only a limited capacity. Their model also accounts for the fact that we remember words from the beginning and end of a list better than from the middle (the serial position effect).

Our brains consist of billions of neurons in densely-interconnected networks, and they control every aspect of our behavior, our movements, thoughts, and feelings. To explore their functioning, theorists have proposed neural network models in which every unit is connected to every other unit. Activity in one will spread to the others, depending on the strength of their connections. A key assumption is that when units are active simultaneously, their connection is strengthened; one formula used to calculate such changes is the delta rule, which is almost identical to the fomula of the Rescorla-Wagner model. These simple networks prove to be surprisingly powerful; they can account for many features of conditioning, concept learning, and memory. One recent development has been deep learning models that incorporate hidden units, between input and output units. This seemingly small innovation has dramatically increased the ability of these models to carry out sophisticated tasks; examples include beating world champions at chess and diagnosing skin cancer. One problem is that learning is slow, and new learning can result in the loss of older information (catastrophic interference). Whatever their ultimate fate, these models have demonstrated the power of even simple networks to perform tasks of astonishing sophistication.