3.5 Perception Flashcards
Researchers recorded the activity of the single nuerons in the visual cortex of monkeys and ferrets
found more neurons that respond best to horizontals and verticals than neurons that respond best to oblique orientations (Coppola et al., 1998; DeValois, Yund, & Hepler, 1982).
Evidence from brain scanning experiments suggests that this occurs in humans as well. For example, Nasr and Tootell (2012) found that the cortical area that is typically involved in scene perception, the so-called parahippocampal place area or PPA, shows higher fMRI activity when squares are presented in vertical or horizontal orientations than when they are presented in oblique orientations (see Figure 3.28). What makes this study interesting is that this selective sensitivity to horizontal and vertical orientations was not observed in any other cortical area, thereby linking the oblique effect to real-world scene perception mediated by the PPA.
Why are there more neurons that respond to horizontals and veticals
One possible answer is based on Darwin’s theory of natural selection, which states that characteristics that enhance an animal’s ability to survive, and therefore reproduce, will be passed on to future generations. Through the process of evolution, organisms whose visual systems contained neurons that fired to important things in the environment (such as verticals and horizontals, which occur frequently in the forest, for example) would be more likely to survive and pass on an enhanced ability to sense verticals and horizontals than would an organism with a visual system that did not contain these specialized neurons. Through this evolutionary process, the visual system may have been shaped to contain neurons that respond to things that are found frequently in the environment (Hansen & Essock, 2004).
Another evidence why we process and respond to horizontals than verticals?
a great deal of evidence that learning can shape the response properties of neurons through a process called experience-dependent plasticity.
What is experience-dependent plasicitity?
A mechanism that causes an organism’s neurons to develop so they respond best to the type of stimulation to which the organism has been exposed.
The mechanism through which the structure of the brain is changed by experience,
How did experience-dependent plasicity demonstrate in animals?
shown that if an animal is reared in a particular environment, neurons in the animal’s brain change so that they become tuned to respond more strongly to specific aspects of that environment.
example, when a kitten is born, its visual cortex contains neurons called feature detectors that respond to oriented bars (see Chapter 2). Normally, the kitten’s brain contains neurons that respond to all orientations, ranging from horizontal to slanted to vertical, and when the kitten grows up into a cat, the cat has neurons that can respond to all orientations.
Blaemore and COOPER answered question that
what would happen if kittens were reared in an environment consisting only of verticals?
Procedure
rearing kittens in a space in which they saw only vertical black and white stripes on the walls. Kittens reared in this vertical environment batted at a moving vertical stick but ignored horizontal objects
What happened in Blakemore and Cooper’s experiment?
The basis of this lack of response to horizontals became clear when recording from neurons in the kitten’s brain revealed that the visual cortex had been reshaped in such a way that it contained neurons that responded mainly to verticals and no neurons that responded to horizontals. Similarly, kittens reared in an environment consisting only of horizontals ended up with a visual cortex that contained neurons that responded mainly to horizontals. Thus, the kitten’s brain had been shaped to respond best to the environment to which it had been exposed (Blakemore & Cooper, 1970; Hirsch & Spinelli, 1970).
How has experience-dependent plasicity also been demonstrated in humans using fMRI
The starting point for this research is the finding that there is an area in the temporal lobe called the fusiform face area (FFA) that contains many neurons that respond best to faces (see Chapter 2). Gauthier, Tarr, Anderson, Skudlarski, & Gore (1999) showed that experience-dependent plasticity may play a role in determining these neurons’ response to faces by measuring the level of activity in the FFA in response to faces and also to objects called “Greebles.” Greebles are families of computer-generated “beings” that all have the same basic configuration but differ in the shapes of their parts (just like faces).
Start of experiment
experience dependent plasicitiy
“Greeble novices” because they did not have had any previous experience with the Greebles), it was found that the faces caused more FFA activity than the Greebles. Gauthier et al. (1999) then gave their participants extensive training over a 4-day period in “Greeble recognition.” These training sessions, which required that each Greeble had to be labelled with a specific name, turned the participants into “Greeble experts.” After the training, it was found that the FFA responded almost as well to Greebles as to faces. These results suggest that the FFA may contain neurons that respond not just to faces but to other complex objects, like the Greebles, as well. It therefore seems that the particular objects to which these neurons respond best are established by experience with the objects. In fact, in other experiments Gauthier and her colleagues have also shown that neurons in the FFA of people who are experts in recognizing cars and birds respond well not only to human faces but also to cars for the car experts and to birds for the bird experts (Gauthier, Skudlarski, Gore, & Anderson, 2000). Thus, just as rearing kittens in a vertical environment increased the number of neurons that responded to verticals, training humans to recognize Greebles, cars or birds causes the FFA to respond more strongly to these objects (see Grill-Spector et al. (2004) for contrasting evidence and an opposing view). The results by Gauthier et al. support the idea that neurons in the FFA respond strongly to faces not just because this was organized this way long before birth, but also because we have a lifetime of experience perceiving faces.
These demonstrations of experience-dependent plasticity in kittens and humans show that the brain’s functioning can be “tuned” to operate best within a specific environment. Thus, continued exposure to things that occur regularly in the environment can cause neurons to become adapted to respond best to these regularities. Looked at in this way, one could say that neurons can reflect knowledge about properties of the environment.
The natural environment contains many horizontal and vertical lines, and research has demonstrated that animals have more neurons that respond to stimuli with horizontal or vertical orientations than neurons that respond to other orientations. To the extent that having more neurons that respond to horizontal or vertical orientations conveys a survival advantage and makes reproduction more likely, it is consistent with
natural selection.
To the extent that having more neurons that respond to horizontal or vertical orientations conveys a survival advantage and makes reproduction more likely, it is consistent with natural selection.
Kittens who are raised in an artificial environment in which they are only exposed to vertical lines subsequently have neurons that respond to vertical lines and none that respond to horizontal lines. This is most consistent with
experience-dependent plasticity.
The mechanism through which the structure of the brain is changed by experience is called experience-dependent plasticity and has been demonstrated in many experiments on animals.
Gauthier demonstrated experience-dependent plasticity in humans by training them to become experts in recognizing “Greebles”, (families of computer generated creatures that have the same general structures but differ in specific features) and using fMRI to measure activity in the participants’
FFA.
Gauthier used fMRI to measure activity in participants’ fusiform face area (FFA).
