Cognitieve psychologie
Part 1 The Foundations of Cognitive Psychology
1 The Science of the Mind
The Scope of Cognitive Psychology
The Broad Role of Memory
Many (perhaps all) of your encounters with the world depend on your supplementing
your experience with knowledge (out of your memory) that you bring to the situation.
Amnesia and Memory Loss
Cognitive psychology can help us understand capacities relevant to every moment of
our lives. Activities that don’t appear to be intellectual would collapse without the support of
our cognitive functioning. The same is true whether we’re considering our physical
movements through the world, our social lives, our emotions, or any other domain.
The Cognitive Revolution
Cognitive psychology is roughly 60 years old (1950s/1960s) and the emergence of
this field was in some ways dramatic. In some ways it was the limitations of the earlier
traditions in psychology that gave rise to cognitive psychology.
The Limits of Introspection
1) Investigators like Wundt and his student Titchener soon had to acknowledge that
some thoughts are unconscious, which meant that introspection was limited as a
research tool -introspection is the study of conscious experiences.
2) Testability of claims is often unattainable (and this is a necessity in science).
The Years of Behaviorism
The concerns described above led many psychologists to abandon introspection as a
research tool. Instead, psychology needed objective data, they argued, and that meant data
out in the open for all to observe. This perspective led to the behaviorist movement, a
movement that dominated psychology in America for the first half of the 20th century.
Although successful, the behaviorist perspective demands that we not talk about
mental entities such as beliefs, memories, and so on, because these things cannot be
studied directly and so cannot be studied scientifically. Yet it seems that these subjective
entities play a pivotal role in guiding behavior (ways people act are guided by how they
understand or interpret the situation, not by the objective situation itself), and so we must
consider them if we want to understand behavior.
The Intellectual Foundations of the Cognitive Revolution
So in order to study the way people act, we need to study the mental world, but we
can’t. Philosopher Immanuel Kant (1724-1804) came with a solution to this impasse with his
transcendental method, in which you begin with the observable facts and work backward
from these observations (e.g. what must be the underlying causes that led to these effects?).
This method, sometimes called “inference to the best explanation”, is at the heart of modern
science.
Mental processes cannot be observed directly, so therefore we should study them
,indirectly, relying on the fact that these processes, themselves invisible, have visible
consequences: measurable delays in producing a response, performances that can be
assessed for accuracy, errors that can be scrutinized and categorized. By examining these
(and other) effects produced by mental processes, we can develop -and test- hypotheses
about what the mental processes must have been.
The Path from Behaviorism to the Cognitive Revolution
European Roots of the Cognitive Revolution
- The Gestalt psychology movement (based in Berlin in the early decades of the 20th
century) fed into and strengthened the cognitive revolution. Gestalt psychologists
argued that behaviors, ideas, and perceptions are organized in a way that cannot be
understood through a part-by-part, element-by-element, analysis of the world.
Instead, the elements take on meaning only as part of the whole -and therefore
psychology needed to understand the nature of the “whole”.
- Tolman’s research demonstrated that even in rats, learning involved the acquisition
of new knowledge and not just a change in behavior.
- Chomsky argued powerfully that a behaviorist analysis was inadequate as an
explanation for language learning and language use.
- Bartlett’s research showed that people spontaneously fit their experiences into a
mental framework, or schema.
Computers and the Cognitive Revolution
In the 1950s, the field of “artificial intelligence” made rapid progress. Psychologists
were intrigued by these developments and began to explore the possibility that the human
mind followed procedures similar to those used in computers.
Research in Cognitive Psychology: The Diversity of Methods
Cognitive psychology uses diverse methods and collects many types of data.
For example, how complete someone’s memory is; how accurate the memory is; speed, by
examining the response time (RT); observations focused on the brain and nervous system
(partnership with cognitive neuroscience: the effort toward understanding humans’ mental
functioning through close study of the brain and nervous system); information about
damaged brains (partnership with clinical neuropsychology: the study of brain function
that uses, as its main data source, cases in which damage or illness has disrupted the
working of some brain structure); information about healthy brains comes from
neuroimaging techniques, which enable us to scrutinize the precise structure of the brain
and to track the moment-by-moment pattern of activation within someone’s brain.
Part 2 Learning About The World Around us
3 Visual Perception
Akinetopsia: an extremely rare disorder in which a patient has lost the ability to
perceive motion in their visual field, despite being able to see stationary objects. Akinetopsia
is attributed to specific lesions in the visual cortex. (patient L. M.).
,The Visual System
The Photoreceptors
Light hits the front surface of the eyeball, passes through the cornea and the lens,
and then hits the retina, the light-sensitive tissue that lines the back of the eyeball (and is
made up of 3 main layers: rods and cones, bipolar cells, ganglion cells (whose axons make
up the optic nerve)). The cornea and lens focus the incoming light, just as a camera lens
might, so that a sharp image is cast onto the retina. The focusing is made possible by a
band of muscle that surrounds the lens (when it tightens, the lens bulges somewhat, the
proper shape is created for focusing the images cast by nearby objects; when it relaxes, the
lens returns to a flatter shape, focus for objects farther away).
On the retina there are two types of photoreceptors -specialized neural cells that
respond directly to the incoming light:
1) rods (sensitive to very low levels of light; play essential role whenever moving around in
semidarkness; color-blind, so can only distinguish different intensities of light);
2) cones (less sensitive than rods, need more light to operate at all; sensitive to color
differences: there are 3 types of cones, each having its own pattern of sensitivities to
different wavelengths (ranging from 400 (violet) to 700 (red) nanometers). You perceive
color by comparing the outputs from these 3 cone types; cones enable you to perceive fine
detail (acuity=ability to see detail); the fovea is the center of the retina, where cones far
outnumber rods (the center of fovea has no rods at all)).
There are neither rods or cones at the retina’s blind spot -the position at which the
neural fibers that make up the optic nerve exit the eyeball (-> no space for any rods/cones).
In portions of the retina more distant from the fovea the rods predominate. This
distribution explains why you’re better able to see very dim lights out of the corner of your
eyes instead of looking right at it.
Lateral Inhibition
Rods and cones do not report directly to the cortex, but stimulate bipolar cells,
which in turn excite ganglion cells. The ganglion cells are spread across the entire retina,
but all of their axons converge to form a bundle of fibers -the optic nerve- which leaves the
eyeball and carries information to a way station in the thalamus -the lateral geniculate
nucleus (LGN)- from which the information is transmitted to the primary projection area for
vision, in the occipital lobe.
Lateral inhibition is a pattern in which cells, when stimulated, inhibit the activity of
neighboring cells. This inhibition actually highlights a surface’s edges, because the response
of cells detecting the edge of the surface will be stronger than that of cells detecting the
middle of the surface (less inhibition (from one side only, while the middle gets inhibition
from both sides). Edge enhancement (due to lateral inhibition of cells in the retina) results in
greater contrast around edges. (The Mach bands are an illusion caused by this process).
Visual Coding
Single Neurons and Single-Cell Recording
Single-cell recording: a technique/procedure through which investigators can
record, moment by moment, the pattern of electrical changes within a single neuron. When a
neuron fires, each response is the same size (all-or-none law), but neurons can vary in how
often they fire. When investigators record the activity of a single neuron, what they’re usually
interested in is the cell’s firing rate in “spikes per second”.
, Multiple Types of Receptive Fields
Center-surrounded cells: cells that fire at their maximum rate when light is
presented in a small, roughly circular area in a specific position within the field of view.
Presentations of light just outside of this area cause the cell to fire at less than its usual
“resting” rate, so the input must be precisely positioned to make this cell fire.
Like this you have different cells, with different orientations (fire only when input
contains a line segment at a certain orientation) which merely define the cells’ “preference”,
because these cells are not oblivious to edges of other orientations. But the farther the edge
is from the cell’s preferred orientation, the weaker the firing will be, and edges sharply
different from the cell’s preferred orientation (e.g. vertical edge for a cell that prefers
horizontal) will elicit virtually no response.
Other cells elsewhere in the visual cortex have receptive fields that are more specific
(angle/movement/etc.).
Parallel Processing in the Visual System
Area V1: the site on the occipital lobe where axons from the LGN first reach the
cortex. Each brain area involved in vision seems to have its own function. E.g., neurons in
Area MT are acutely sensitive to direction and speed of movement (damage in akinetopsia).
Cells in Area V4 fire most strongly when the input is of a certain color and a certain shape.
The visual system relies on parallel processing, with many different steps (different
kinds of analysis, like the simultaneous detection from Area MT of movement and Area V4 of
shapes) going on simultaneously. Serial processing is processing in which steps are
carried out one at a time -i.e. in a series.
Parallel processing is also evident when we move beyond the occipital cortex: some
of the activation from the occipital lobe is passed along to the cortex of the temporal lobe.
This what system plays a major role in the identification of visual objects. At the same time,
activation from the occipital lobe is also passed along a second pathway, leading to the
parietal cortex, called the where system, that guides your action based on your perception
of where objects are located.
Putting the Pieces Back Together
Binding problem: the task of reuniting the various elements of a scene, elements
that are initially addressed by different systems in different parts of the brain. Obviously this
problem is solved: what you perceive is not an unordered catalog of sensory elements,
instead, you perceive a coherent, integrated perceptual world.
Visual Maps and Firing Synchrony
Neural synchrony: if the neurons detecting a vertical line are firing in synchrony with
those signaling movement, then these attributes are registered as belonging to the same
object. If they aren’t in synchrony, then the features aren’t bound together.
Evidence for the crucial role of attention in binding together the separate features of a
stimulus is for example seen in the fact that when we overload perceivers’ attention, they
often make conjunction errors. This means that they correctly detect the features present
in a visual display, but then make mistakes about how the features are bound together (e.g.
see blue H, red T and say you saw red H, blue T).
Concluding, information represented in the brain is reflected in which cells are firing,
how often they are firing, whether the cells are firing in synchrony with other cells, and the
rhythm in which they are firing.
