Unconscious Learning

A. Simple Forms of Learning

In this section, we will explore several "simple" (i.e., nonassociative) forms of learning. Keep in mind that even those forms of learning that exhibit themselves in a fairly straightforward manner at the behavioral level involve elaborate underlying cellular and molecular machinery. In this section, we will emphasize that several forms of nonassociative learning are exhibited by animals, including: habituation, dishabituation, and sensitization (see Figure 6). These forms of learning involve altered responses to a single stimulus and do not necessitate the animal forming any association between one environmental stimulus and another; that is, these forms of learning are nonassociative. They also can occur unconsciously (see Figure 2), generally requiring neither conscious perception of environmental stimuli nor conscious recall of information.

Perhaps the simplest form of learning in existence is habituation. When an animal is repeatedly presented with an innocuous environmental stimulus, over time the animal's response to that stimulus decrements. For example, if someone from a small, quiet town moves to a street-level apartment in Manhattan, the street noises in the big city are typically disturbing at first. However, over time, the newcomer becomes accustomed to the new environment, and the street noise is no longer so bothersome. This type of phenomenon is referred to as habituation. The teleologic explanation for habituation is that over time animals learn to ignore environmental stimuli that carry no unique informational content.

Habituation is a very robust behavioral phenomenon that exhibits itself in many forms—essentially all baseline behavioral responses more complex than the purest reflex responses habituate. Some of the more well-studied habituation phenomena experimentally are habituation of the Aplysia californica gill-and-syphon defensive withdrawal response and habituation of reflexive leg-lifting in Drosophila. Habit-uation is also frequently encountered outside the laboratory setting; in particular,

FIGURE 6 Some simple nonassociative forms of learning. Habituation, dishabituation, and sensitization are illustrated. Each circle represents a hypothetical response to an environmental stimulus. Habituation is a decrease in response (arbitrarily defined in this schematic example) with repeated presentation of the stimulus. Dishabituation is a recovery to normal baseline response when the animal receives a different environmental stimulus. Sensitization is an increase in the magnitude of the response above the original baseline.

FIGURE 6 Some simple nonassociative forms of learning. Habituation, dishabituation, and sensitization are illustrated. Each circle represents a hypothetical response to an environmental stimulus. Habituation is a decrease in response (arbitrarily defined in this schematic example) with repeated presentation of the stimulus. Dishabituation is a recovery to normal baseline response when the animal receives a different environmental stimulus. Sensitization is an increase in the magnitude of the response above the original baseline.

it is frequently observed by teachers in the classroom lecture environment.

After a response is habituated, if you present another, unique stimulus, dishabit-uation can occur. For example, even after becoming habituated to street noises, if one is expecting a visitor to be dropped off at their doorstep, street noises may once again become noticeable. It is worth noting that dishabituation is a useful tool to distinguish habituation from fatigue. A habituated response can be overcome by a dishabituating stimulus; however, a decreased response due to fatigue cannot.

Animals can also learn to become hyper-responsive to an environmental stimulus, a phenomenon known as sensitization. Sensitization is defined as an increased response over and above the normal baseline response, that occurs in response to an environmental signal. Sensitizing stimuli typically can elicit an augmentation in response from either a nonhabituated or a habituated starting point. In the second scenario, a component of the increased responsiveness must, by definition, then be described as dishabituation (see Figure 6).

Keep in mind that in some ways the definitions of habituation, dishabituation, and sensitization are arbitrary. In the natural setting, animals are constantly modifying their behaviors in response to the ongoing barrage of environmental signals. Thus, it is difficult to determine what a "baseline" response is outside of a stringently controlled experimental setting.

All of these nonassociative forms of learning can exhibit themselves in either short- or long-term forms. The duration of the memory for a learned event depends on the number of times an animal experiences a behavior-modifying stimulus. For example, a single sensitizing stimulation may elicit sensitization that lasts only a few minutes, whereas repeated stimulations will likely result in sensitization lasting hours to days (see Figure 1.4, for example). Repeated presentations of multiple training trials can elicit sensitization lasting for weeks.

One exciting area of contemporary neurobiological research is to try to understand the basis for short- and long-term nonassociative learning. Starting in the 1960s, the mechanisms underlying habit-uation and sensitization began to be worked out at the cellular and biochemical level. Part of this watershed of new understanding of the basis of learning and memory came about as a result of the insight to capitalize on easily studied, simple forms of learning in special preparations that lent themselves to experimental investigation at the cellular level. In particular, the work of Eric Kandel (Figure 7) and his colleagues allowed enormous progress in our understanding of the cellular basis of behavior in general, and learning and memory specifically. Kandel and his colleagues—Jimmy Schwartz, Vince Castellucci, Jack Byrne, Tom Carew, and Bob Hawkins, along with many others— have used the simple marine mollusk Aplysia californica (Figure 8) to great effect to study the behavioral attributes and cellular and molecular mechanisms of learning and memory.

Eric Kellerman Figure Studies
FIGURE 7 Dr. Eric Kandel. Kandel is a University Professor at Columbia University and Nobel Prizewinner who led pioneering studies on the cellular basis of learning and memory. Reprinted with permission.
Aplysia Californica
FIGURE 8 Aplysia californica. Aplysia, a nudibranch mollusk found in the cool waters off the coast of Calfornia, is popularized for its use in studies of simple forms of learning and memory. Photo courtesy of Dr. John Byrne, UT Houston.

A few words about the particulars of the Aplysia model system are appropriate at this point because we will refer to this system at later points in the book. Much (but by no means all) of the work in Aplysia has been geared toward understanding the basis of sensitization in this animal. Aplysia has on its dorsum a respiratory gill and siphon complex, which is normally extended when the animal is in the resting state. Lightly touching the gill or siphon (or experimentally squirting it with a Water-Pic) elicits a defensive withdrawal reflex in order to protect the gill from potential damage. This defensive withdrawal reflex can undergo both habituation (by repeated light stimuli) and sensitization. Sensitization occurs when the animal receives an aversive stimulus, for example a modest tail-shock experimentally or a predatory nip in the wild (see Box 3). After sensitizing stimulation, the animal exhibits a more robust, longer-lasting gill-withdrawal in response to the identical light touch or water squirt. Acquisition of this sensitization response is graded; repetitive sensitizing stimuli can give sensitization lasting minutes to hours (one to a few shocks) or weeks (repeated training trials over a few days) (see Figure 4). We will return to the Aplysia system in the later chapters of the book, where we

Was this article helpful?

0 0
Eliminating Stress and Anxiety From Your Life

Eliminating Stress and Anxiety From Your Life

It seems like you hear it all the time from nearly every one you know I'm SO stressed out!? Pressures abound in this world today. Those pressures cause stress and anxiety, and often we are ill-equipped to deal with those stressors that trigger anxiety and other feelings that can make us sick. Literally, sick.

Get My Free Ebook


Post a comment