Cognitive Psychology 2. Visual Perception
How we sense and represent the world?
We do not perceive the world exactly as our eyes see it Our brain tries to make sense of the many stimuli that enter our eyes and fall on our retina It gives stimuli meaning and interpreting them
Where ganglion cells go after chiasma?
After being routed (nukreiptos) via the optic chiasma, about 90% of the ganglion cells then go the lateral geniculate nucleus of the thalamus
How we recognize objects?
Before you recognize it, you correctly sensed all aspects of the figure these sensations are Not yet organized to form a mental percept (you dont see a cow)- a mental representation (sensations have meaning)of a stimulus that is perceived The role of experience (if you have previous experience it is easier to understand, percieve something) Sometimes we cannot perceive what does exist
Are the triangles really there?
Both triangles are optical illusions. Sometimes we perceive things that do not exist.
How do we actually perceive what we see? theories:
Bottom-up theories Perception starts with the stimuli whose appearance you take in through your eye Data-driven Top-down theories Perception id driven by high-level cognitive processes, existing knowledge, ,and the prior expectations that influence perception (Clark, 2003)
Bottom-up theories. How Do We Make Sense of What We See?
Direct Perception - Gibson's theory Template Theories Feature-Matching Theories Recognition-by-Components Theory
rods and cones
Each eye contains roughly 120 million rods and 8 million cones Rods and cones differ not only in shape but also in their compositions, location, and responses to light Within the rods and cones are photopigments, chemical substances that react to light and transform physical electromagnetic energy into an electrochemical neural impulse that can be understood by the brain
James Gibson (1904-1979)
He provided a useful framework for studying perception Distal (external) object -The object in the external world (e.g., a falling tree) Information medium -The event of the tree falling, sound waves, as in the sound of a falling tree It might also be reflected light, chemical molecules, or tactile information coming from the environment
Recognition-by-Components Theory
It explains our ability to perceive 3-D objects with the help of simple geometric shapes Seeing with the Help of Geons We achieve this by manipulating a number of simple 3-D geometric shapes called geons (for geometrical ions) - bricks, cylinders, wedges, cones, and their curved axis counterparts (Biederman, 1990/1993b) We quickly recognize objects by observing the edges of them and then decomposing the objects into geons The geons are simple and are viewpoint-invariant (i.e., distinct from various viewpoints) The RBC theory explains how we may recognize general instances of chairs, lamps, and faces, but it does don adequately explain how we recognize particular chairs or particular faces Neurons in the inferior temporal cortex are sensitive to viewpoint-dependent properties
Proximal (near) stimulation
It occurs when the information from light waves come into contact with the appropriate sensory receptors of the eyes (i.e., the cells in your retina absorb the light waves)
What happens when light focuses on the retina? and how electromagnetic energy is converted into neural electrochemical impulses?
Neurochemical messages by the rods and cones travel via the bipolar cells to the ganglion cells The axons of the ganglion cells in the eye collectively form the optic nerve for that eye The optic nerves of the two eyes join at the base of the brain to form the optic chiasma The ganglion cells from the inward, or nasal, part of the retina - the part closer to your nose - cross through the optic chiasma and extend to the opposite hemisphere of the brain The ganglion cells from the outward, or temporal area of the retina closer to your temple go to the hemisphere on the same side of the body
Is what we sense necessarily what we perceive?
No, Perceptual illusions suggest that what we sense is not necessarily what we perceive. Our minds should take the available sensory information and manipulating that information somehow to create mental representations of objects, properties, and spatial relationships within our environments (Peterson, 1999).
Can we experience the same stimnulus twice?
No, we never can experience through vision, hearing, taste, smell or touch exactly the same set of stimulus properties we have experienced before. Every apple casts a somewhat different image on our retina
"where" pathway
One ascends (goes up, pakyla) toward the parietal lobe, along the dorsal pathway or where pathway Responsible for processing location and motion information
what pathway
One descends (goes down, nusileidžia) to the temporal lobe, along the ventral pathway or what pathway Responsible for processing the color, shape, and identity of visual stimuli
Rods
Rods: Long and thin photoreceptors More highly concentrated in the periphery of the retina than in the foveal region Responsible for night vision and are sensitive to light and dark stimuli
How do we achieve perceptual stability in the face of this utter instability at the level of sensory receptors?
Sensory systems adapt to the stimulation. it seems the same: Variation seems even necessary for perception Sensory adaptation ensures that sensory information is changing constantly When your eyes are exposed to a uniform (vienodas) field of stimulation (e.g., a clear blue sky) , you will stop receiving the stimulus after a few minutes and see just a gray filed instead. This is because your eyes have adapted to the stimulus.
Cones
Short and thick photoreceptors They allow for the perception of color More highly concentrated in the foveal region than in the periphery of the retina
The what/how hypothesis (what they are and how they function; Goodale & Milner, 2004; Goodale & Westwood, 2004
Spatial information about where something is located in space is always present in visual information processing What differs between the two pathways is whether the emphasis is on identifying what an object is or, instead, on how we can situate ourselves so as to grasp the object The what pathway is in the ventral stream and is responsible for the identification of objects
amacrine cells
Specialized retinal cells that contact both the bipolar cells and the ganglion cells, and are especially significant in inhibitory interactions within the retina.
how pathway
The how pathway is located in the dorsal stream and controls movements in relation to the objects that have been identified through the "what" pathway
Direct Perception - Gibson's theory
The information in our sensory receptors, including the sensory context, is all we need to perceive anything The environment supplies us with all the information we need for perception - ecological perception Higher-cognitive processes or anything else is not necessary Recognizing other's emotions and intentions (Gallagher, 2008) 30 to 100 milliseconds after a visual stimulus, mirror neurons start firing Mirror neurons are active both when one acts and when observing the same act performed by somebody else Before we realize what we are perceiving, we may already be able to understand the expressions, emotions, and movements of the person we observe (Gallagher, 2008)
First layer of retina:
The layer of ganglion cells, whose axons constitute (sudaro) the optic nerve It is closest to the front, outward-facing surface of the eye
image projection into the ratina?
The lens of each eye naturally inverts the image of the world as it projects the image onto the retina Therefore, the message sent to your brain is literally upside-down and backward
What are the visual pathways in the brain?
The path the visual information takes from its entering the human perceptual system through the eyes to its being completely processed
How Does Our Visual System Work? What is the precondition for vision?
The precondition for vision is the existence of light
The retina is:
The retina is only about as thick as a single page of a book and it consists of three layers
Scond layer of retina:
The second layer consists of three kinds of interneuron cells: 1. Amacrine cells 2. Horizontal cells 3. Bipolar cells
Third layer of retina:
The third layer contains photoreceptors (rods and cones) which convert light into electrochemical energy that is transmitted by neurons to the brain
Where to draw the line between perception (suvokiams) and cognition (pažinimas) or between sensation (jutimas) and perception?
These processes are part of a continuum Questions of sensation focus on qualities of stimulation (e.g., Is that red shade brighter than the red of an apple?, How well do one person's impressions of colors or sounds match someone else's impressions of those same colors or sounds?) This same color or sound information answers different questions for perception Typically questions of identity and of form, pattern, and movement (e.g., Is that red thing an apple?) Cognition occurs as this information is used to serve further goals (e.g., Is that apple edible?)
Horizontal cells
These two kinds of cells make single lateral (i.e., horizontal) connections among adjacent (gretimas) areas of the retina in the middle layer of cells
The what/where hypothesis (where they are)
Two pathways because information from the visual cortex in the occipital lobe is forwarded through two fasciculi (fiber bundles)
How Does Our Visual System Work?
Vision begins when light passes through the protective covering of the eye Protective covering: The cornea Then light passes through the pupil, the opening in the center of the iris It continuous through the crystalline lens and the vitreous humor, a gel-like structure that comprises the majority of the eye Eventually, the light focuses on the retina and electromagnetic energy is converted into neural electrochemical impulses (Blake, 2000)
Where is the vision is most acute ?
Vision is most acute in the fovea, which is a small, thin region on the retina, the size of the head of a pin When you look straight at an object, your eyes rotate so that the image falls directly onto the fovea
Feature-Matching Theories
We attempt to match features of a pattern of features stores in memory, rather than to match a whole pattern to a template or a prototype (Stankiewicz, 2003) The Pandemoniun Model Image aspects, feature aspects, cognitive aspects, and decision aspects receive and analyze the features of a stimulus Image aspects: Receives sensory input Feature aspects: Decode specific features Cognitive aspects: "Shout" when they receive certain combinations of features Decision aspects: "Listen" for the loudest shout in pandemonium to identify input The visual cortex contains neurons that respond only to a particular kind of stimulus (e.g., a horizontal line), and only if that stimulus fell onto a specific region of the retina.
Template Theories
We have stored in our minds myriad sets of templates Highly detailed models for patterns we potentially might recognize We recognize a pattern by comparing it with our set of templates We then chose the exact template that perfectly matches what we observe (Selfridge & Neisser, 1960) Expertise is attained by acquiring chunks of knowledge in long-term memory that can later be accessed for fast recognition Does it make a difference to our brain whether we perceive letters or digits? An area on or near the left fusiform gyrus that is activates significantly more when a person is presented with letters than with digits
Perceptual object
What you see Perception occurs when a perceptual object is created in you that reflects the external world An image of a falling tree is created on your retina that reflects the falling tree that is in front of you
3 layers of retina:
ganglion cells, interneuron cells, photoreceptors
Visual cortex
it contains several processing areas Each area handles different kinds of information relating to intensity and quality, including color, location, depth, pattern, and form
From the thalamus , neurons carry information to the...
primary visual cortex (V1 or striate cortex) in the occipital lobe of the brain
Bipolar cells
they make dual connections forward and outward to the ganglion cells, as well as backward and inward to the third layer of retinal cells
