PERCEPTION

Perception
- experiences resulting from stimulation of the senses.

SOME BASIC CHARACTERISTICS OF PERCEPTION

  1. illustrates how perception can change based on added information

  2. illustrates how perception can be based on a perceptual rule

  3. how perception can involve a process similar to reasoning or problem-solving

  4. how arriving at a perception can involve a process.

  5. how perception occurs in conjunction with action.

A HUMAN PERCEIVES OBJECTS AND A SCENE

A COMPUTER VISION SYSTEM PERCEIVES OBJECTS AND A SCENE

1950S
- Scientists thought they could build a machine with human-like vision in just a few years. But early systems were very slow and could barely identify simple objects.

1987
- The International Journal of Computer Vision, the first journal devoted solely to computer vision, was founded. Researchers were still struggling to solve basic visual problems, using complex math to understand things that are easy for humans.

2004
-thirteen robotic vehicles are lined up in the Mojave Desert in California for the Defense Advanced Projects Agency (DARPA) Grand Challenge. The tasks was to drive 150 miles from starting point to Las VEGAS, using only gps coordinates to define the course and computer vision to avoid obstacles.

WHY IS IT SO DIFFICULT TO DESIGN A PERCEIVING MACHINE?

  1. THE STIMULUS ON THE RECEPTORS IS AMBIGOUS.

Inverse projection problem
- task of determining the object responsible for a particular image on the retina.

  1. OBJECTS CAN BE HIDDEN OR BLURRED

  2. OBJECTS LOOK DIFFERENT FROM DIFFERENT VIEWPOINTS

viewpoint invariance
- People’s ability to recognize an object even when it is seen from a different viewpoint.

  1. SCENES CONTAINING HIGH-LEVEL INFORMATION

INFORMATION FOR HUMAN PERCEPTION

  • Bottom-up processing
    - sequence of events from eye to brain.

  • Top-down processing

-processing that originates in the brain at the top of the perceptual system.

2 EXAMPLES OF TOP DOWN PROCESSING.

  1. PERCEIVING OBJECTS
    - We perceive the blobs as different objects because of our knowledge of the kinds of objects that are likely to be found in different types of scenes.

  2. HEARING WORDS IN A SENTENCE

  • Speech segmentation
    - The ability to tell when one word in a conversation ends and the next one begins.

  • Transitional probabilities
    - the likelihood that one sound will follow another within a word.

  • Statistical learning
    - The process of learning about transitional probabilities and about other characteristics of language.

    CONCEPTIONS OF OBJECT PERCEPTION.

HELMHOLTZ’S THEORY OF UNCONSCIOUS INFERENCE

Hermann von Helmholtz
- was a physicist who made important contributions to fields as diverse as thermodynamics, nerve physiology, visual perception, and aesthetics.
- he invented ophthalmoscope, versions of which are still used today to enable physician to examine the blood vessels inside the eyes.

  • likelihood principle
    - we perceive the object that is most likely to have caused the pattern of stimuli we have received.

  • unconscious inference
    - our perceptions are the result of unconscious assumptions, or inferences, that we make about the environment.

THE GESTALT PRINCIPLES OF ORGANIZATION

  • The gestalt approach to perception originated, in part, as a reaction to Wilhelm Wundt’s structuralism.

Max Wertheimer
- he wondered how the structuralist idea that experience is created from sensations could explain the illusion of movement he observed in a stroboscope.

Apparent Movement
- an optical illusion in which stationary objects viewed in quick succession or in relation to moving objects appear to be in motion.
- although movement is perceived, nothing is actually moving.

THREE COMPONENTS TO STIMULI THAT CREATE APPARENT MOVEMENT:

  1. One light flashes on and off

  2. there is a period of darkness lasting a fraction of a second

  3. the second light flashes on and off.

Wertheimer’s conclusions from the phenomenon of apparent movement

  1. Apparent movement cannot be explained by sensations because there is nothing in the dark space between the flashing lights.

  2. The whole is different than the sum of its parts.

GOOD CONTINUATION

  • principle of good continuation
    - points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the lines tend to be seen in such a way as to follow the smoothest path.

  • law of pragnanz, also called the principle of good figure/principle of simplicity
    - every stimulus pattern is seen in such a way that the resulting structure is as simple as possible

  • principle of similarity
    - similar things appeared to be grouped together.

main message: gestalt psychologist realized that perception is based on more than just the pattern of light and dark on the retina, perception is determined by specific organizing principle.

TAKING REGULARITIES OF THE ENVIRONMENT INTO ACCOUNT

  • Regularities in the environment
    - characteristics of the environment that occurs frequently

  • Physical regularities
    - regularly occuring physical properties of the environment. (sky, trees and plants).

  • Oblique effect
    - people can perceive horizontals and verticals more easily than other orientations.

  • light-from-above assumption
    - we usually assume that light is coming from above, because light in our environment, including the sun and most artificial light, usually comes above.


note: One of the reasons humans are able to perceive and recog nize objects and scenes so much better than computer-guided robots is that our system is adapted to respond to the physical characteristics of our environment, such as the orientations of objects and the direction of light.

  • semantic regularities
    - characteristics associated with the function carried out in different types of scenes.

  • Scene schema
    - knowledge of what a given scene typically contains
    - expectations created by scene schemas contribute to our ability to perceive objects and scenes.

BAYESIAN INFERENCE

was named after Thomas Bayes, who proposed that our estimate of the probability of an outcome is determined by prior and likelihood.

  • prior probability
    - our initial belief about the probability of an outcome

  • likelihood
    -the extent to which the available evidence is consistent with the outcome.


note: researchers have used Bayesian Inference to develop computer-vision systems that can apply knowledge about the environment to more accurately translate the pattern of stimulation on their sensors into conclusions about the environment.

NEURONS AND KNOWLEDGE ABOUT THE ENVIRONMENT

NEURONS THAT RESPOND TO HORIZONTAL AND VERTICAL

  • Theory of natural selection
    - states that characteristics that enhance an animal’s ability to survive and, therefore, reproduce will be passed on to future generations

  • Experience-dependent plasticity
    - refers to the ability of the brain to change and adapt its structure and function based on experience.

  • Fusiform Face Area
    - an area in the temporal lobe that contains many neurons that respond best to faces.

PERCEPTION AND ACTION: BEHAVIOR

MOVEMENT FACILITATES PERCEPTION

  • Moving reveals aspects of the objects that are not apparent from a single viewpoint.

  • seeing an object from different viewpoint provides added information that results in more accurate perception, especially for objects that are out of the ordinary.

THE INTERACTION OF PERCEPTION AND ACTION

  • Movement is also important because of the coordination that continually occurs between perceiving stimuli and taking action toward these stimuli.

PERCEPTION AND ACTION: PHYSIOLOGY

two processing streams in the brain

  1. perceiving objects.

  2. locating and taking action toward these objects.

brain ablation
- the study of the effect of removing parts of the brain in animals

neuropsychology
- the study of the behavior of people with brain damage.

WHAT AND WHERE

1982

  • Object discrimination problem
    - the challenge of recognizing and remembering objects in different contexts. It involves a task where an individual must identify objects among others.

  • landmark discrimination problem

  • Parietal
    - where pathway (dorsal/back)

  • Temporal
    -what pathway (ventral/lower part)

PERCEPTION AND ACTION STREAMS

1995

  • David Milner and Melvyn Goodale (1995) used the neuropsychological approach (studying the behavior of people with brain damage) to reveal two streams, one involving the temporal lobe and the other involving the parietal lobe.

  • Parietal
    - action pathway

  • Temporal
    - perception pathway

MIRROR NEURONS
- —neurons that respond both when a monkey observes someone else grasping an object such as food on a tray and when the monkey itself grasps the food

What is the purpose of mirror neurons?

  • they are involved in determining the goal or intention behind the action

SOMETHING TO CONSIDER: KNOWLEDGE, INFERENCE, AND PREDICTION

KNOWLEDGE AND INFERENCE

  • Knowledge
    - forms the basis of unconscious inference and helps interpret sensory information (e.g., recognizing words in a conversation).

  • Inference
    -uses knowledge to predict and make sense of the world (e.g., identifying objects like a book or loaf of bread)

  • Prediction
    -shape how we perceive and interact with the world, as seen in the size-weight illusion, where larger objects seem lighter due to prior predictions about size and weight