What is the lecture mainly about? Why does the professor say Walter Freeman mentioned two types of crowds?

Listen to lecture on the process of memory.
    Professor:
    A popular saying goes, "An elephant never forgets." But how about people? Have you ever forgotten the name of someone you just met at a party? Sure, we all have. This is because our memories are complex processes.
    We’re not going to talk much about the physiology of memory here… both because, well, it’s not our subject, and because there’s a lot we still need to learn about how the brain stores things. One thing we know is that the mechanism isn’t simple. When researchers scan the brain as a memory is forming, parts seem to light up—by "light up" I mean, you know, become active— in random, scattered formations. But of course they can’t be random because memory produces very orderly results.
    One researcher… this is Walter Freeman of the University of California at Berkeley… compares it to two kinds of crowds. The impulses in the brain look completely random, like the movement of a mob of people who are frightened. You know, they just keep moving, and they’re not really going anywhere, and there’s no pattern to their movement. That’s the way impulses in the brain look at first. But since memory does, in fact, work, the impulses must be moving more like people in a crowded train station. You know, if you’ve got people running in and out and from one train line to another, it seems like complete confusion. But really they all know where they’re going. They’re following a set of instructions— the timetable for the trains, the board that tells which track is for which train, all that stuff. So you have to look carefully to see that there’s actually an organization, a system, involved. That’s how memory impulses must function. Freeman figures we just haven’t figured out what the timetable and track numbers are!
    So we’ll leave the physiology there; we’re going to talk about the psychology of memory… the actual process. Psychologists divide memory into three stages: registration, long-term retention, and recall.
    In the initial stage, registration, information is perceived and understood, like when you first hear a name or address. This information is then retained in the short-term memory system. Unfortunately, the short-term memory is limited in the amount of material it can store at one time. And, unless refreshed by constant repetition, the new contents are lost within minutes when replaced by even newer information. To solve this dilemma, the information needs to be transformed into the second stage, long-term retention.
    The conversion to the long-term retention stage is most easily accomplished using what the research team labeled association. Associating the new information with the visual imagery evoked by it gives the individual a sort of "memory" crutch to rely on. For example, let’s say you’re at a party, and you’ve just met a woman named Lily. To remember her name, visualize it in connection to the flower, the lily. Oh, and be sure to make it outlandish… kind of silly, even. Those images are most memorable. Picture her with a big basket of lilies, or wearing a hat with a lily on it, or even sitting inside a giant lily.
    The third stage, recall, is when the information stored—stored through long-term retention—at an unconscious level is then deliberately brought into the conscious mind. However, this final stage primarily depends on how well the material was stored in stage two. Of course, there are disturbances that may affect the recall stage—age, for example. The older a person gets, the less new information he can recall. Disuse is another example. Here, forgetting occurs because stored information is not used and, therefore, is lost. Memory loss can also be physiological. If a person receives an injury to the head, he may experience what is known as amnesia, the failure to remember certain or even all events preceding the accident.
    Of course, many self-help books on how to improve your memory have been published, and many other mnemonic methods have been tried and tested. Let’s take a closer look at some of the more widely accepted approaches to memory enhancement. Perhaps you may even incorporate some of them into your study habits as you prepare for the upcoming finals.