Perception

-The role of perception is to make sense of sensation

-Refers to the overall process of apprehending objects and events in the external environment, to sense them, understand them, identify and label them, and prepare to react to them

3 Stages of Perception:

• Sensation
• Perceptual Organization
• Identification/Recognition of Objects

1) Sensation

-the conversion of physical energy into the neural codes recognized by your brain -the first representation of basic facts of the visual field

2) Perceptual Organization

-The percept of an object is developed

–Provides estimates of an object’s likely size, shape, movement, distance and orientation

-This integrates your past knowledge with the present evidence

-Involves synthesis (integration and combination) of simple sensory features Phappens quickly and without conscious awareness)

3) Identification and Recognition

–Assigns meaning to percepts

-Involves higher level processing: your theories, memories, values, beliefs and attitudes concerning the object

-ex: circular objects become baseballs, coins, clocks, oranges

The Proximal and Distal Stimulus

Proximal Stimulus: the optical image on the retina Pproximate, or near to the observer) Distal Stimulus: the physical object in the world Pdistant from the observer) -Perception involves using information in the proximal stimulus to tell you about the distal stimulus

The Retinal Image

-It is 2-dimensional P2D)

The Environment

-It is 3-dimensional P3D)

Bottom-Up Processing PPRESENT)

-Occurs when the perceptual representation is derived from the information available in the sensory input

Top-Down Processing PPAST)

-Occurs when the perceptual representation is affected by an individuals past knowledge, experience, motivation, etc.

Ambiguity

-Critical information is missing

-Shows that a single image at the sensory level can result in multiple interpretations at the perceptual and identification levels

-Examples: Duck/Rabbit figure, Vase/Faces image, Necker Cube image.

–Instability of ambiguous figures arises when your perception flips back and forth to the two different alternative images

Illusions

-When your perceptual systems actually deceive you into experiencing a stimulus pattern in a manner that is demonstrably incorrect

-Illusions are shared perceptual experiences because of our shared physiology -Illusions point out the discrepancy between percept and reality.

J. J. Oppel

-the first scientific analyzer of illusions

-Geometrical Optical Illusion: when an array of lines are in segments together they look longer than just one or two lines at opposite ends.

The Hermann Grid

-Two ganglion-cell receptive fields are projected onto the grid

–Lateral Inhibition: the cell at the center receives more light and can respond at a lower level because of the greater lateral inhibition by the surround Pmore light = more lateral inhibition)

Illusions in Reality

-they are a part of everyday life Pinescapable)

-TV and lighting, the moon, architects and engineers’ manipulations, etc. – these are just some examples of everyday things that have illusions

Helmholtz’s Classical Theory

-the importance of experience (nurture)

-perception is an inductive process, from specific images to inferences Pspecific  general)

-Helmholtz termed this inductive process: unconscious inference

 Helmholtz’s theory breaks down into two stages  :

• analytic (senses)
• synthetic (integration and synthesis)

-Your interpretations are informed guesses about your perceptions

The Gestalt Approach

-The importance of nature

-Gestalt means “whole”

-Psychological phenomena can only be understood when viewed as organized, structured wholes, and not when broken down into perceptual elements

James Gibson’s Ecological Optics

-Perception can be understood through an analysis of the immediately surrounding environment, or its ecology

-Perceiving = active exploration of the environment

-Gibson states that perception is direct and you don’t need to look for higher processes.

-Humans evolved to detect perception of invariances because it was important for survival

3 Levels of Analysis for Perception

• What are the physiological mechanisms involved in perception?
• What is the process of perceiving?
• What are the properties of the physical world that allow you to perceive?

Attentional Processes

-Attention selectively highlights objects and stimuli in your environment

Selective Attention

-The capacity of reacting to certain stimuli selectively when several occur simultaneously

Goal-Directed Selection

-Choices you make about objects that you’d like to attend as a function of your own goals -You explicitly choose objects for particular scrutiny

Stimulus-Driven Capture

-Occurs when features of the stimuli automatically capture your attention

-This has nothing to do with the goals you have

-Your attention is drawn to new objects in your environment

-Ex: an “H” is written but has an “s” in the middle – this makes it harder to perceive it as an H.

Processes of Perceptual Organization

-The processes that put sensory information together to give you the perception of coherence -What a person experiences as a result of perceptual processing is called a percept

Region Segregation

-combining the outputs of the separate receptors into appropriate larger units

-primary information comes from color and texture

Hubel and Wiesel

-researchers in feature-detectors cells Pi.e. simple cells, complex cells) in receptive fields

Figure

-An objectlike region in the forefront

Ground -seen as the background against which the figures stand out

Closure

-makes you see incomplete figures as complete

-i.e. if a triangle’s lines are not filled in, you perceive it as a full triangle anyway

Figural Goodness Por the Law of Symmetry)

-a concept that includes perceived simplicity, symmetry and regularity

-shapes that are nice and complete are coded more quickly than the “bad” ones

Reference Frames

-The way things are oriented is how you perceive the shape

Max Wertheimer

-A Gestalt psychologist

Wertheimer’s Law of Proximity

-Objects that are near each other tend to be grouped together.

Wertheimer’s Law of Similarity

-All else being equal, the most similar elements are grouper together

Wertheimer’s Law of Common Fate

-All else being equal, elements moving in the same direction and at the same rate are grouped together

Law of Pragnanz Pgood figure)

-A Gestalt Law: you perceive the simplest organization that fits the stimulus pattern

Impossible Figures

-the pieces don’t fit together, or the perceptual staircase goes up and down, it does not make sense

Motion Perception

-When the image on your retina gets bigger = the person is coming near to you

Induces Motion

-when your eyes are still and fixed on the dot -ex: the moon

Apparent Motion

-occurs when 2 stationary spots of light in different positions in the visual field are turned on and off alternatively 4 to 5 times per second -Ex: Phi Phenomenon

Depth Perception

-Depth and Direction

-The visual system has to rely on the retina which makes 2D images, not 3D -Depth perception requires an interpretation of sensory input and experience

-Requires depth cues: binocular cues, motion cues and pictorial cues

Binocular cues and Motion Cues

Binocular disparity:

-The displacement between the horizontal positions of corresponding images in your two eyes

Pretinal disparity: what your two eyes see in distance in depth between two objects)

**The visual system interprets these horizontal positions between your two eyes as 3D images Convergence: -Visual angles

Relative Motion Parallax:

-Provides information about depth because as you move the relative distances of objects in the world determine the amount and direction of relative motion in your retinal image

-As we move, objects that are closer to us move farther across our field of view than do objects that are in the distance.

-As an example, if you’re riding in a car, objects that are close to you seem to go by really quickly Pfor example, a road sign that you pass), but objects that are further away appear to move much more slowly.

Pictorial Cues:

-You can detect depth perception from features in pictures that give us information on space, depth and distance.

-Can be detected from just one eye or both.

Interposition/Occlusion

-when an opaque object blocks out part of a second object

Size/Distance Relation

-the closest object = largest image

-the farther object = smallest image

Linear Perspective

-Convergence of parallel lines

-Convergence IMPLIES distance

Relative Size

-Objects look smaller as they get more and more distant

Ponzo Illusion

-Parallel lines like railroad tracks appear to converge in the distance but actually remain the same distance apart in reality -Shows linear perspective

Texture Gradients

-the phenomena that closer objects have more detail than those farther away giving us more information about distance

Perceptual Constancy

-We see the world as invariant, constant and stable despite changes in the stimulation of our sensory receptors

Size Constancy

-Your ability to perceive the true size of an object despite variations in the size of its retinal image

-It has to do with experience too. Ex: your knowledge of the world proves to your eyes that you know the size of a dog even though it is far away

Ames Room

-A specially constructed room in which all the visible features have been distorted to make the room appear rectangular from one specific point of observation

Shape Constancy

-The perceived shape is unchanged and is not affected by the changes in the retinal image -Like size constancy – you know the shape from your depth perception and also from past knowledge

Orientation Constancy

-Your ability to recognize the true orientation of the figure in the real world even though its orientation in the retinal image is changed

Bottom-Up Processing

-analysis of relevant information

-data-driven processing Pyou receive sensory information from the environment)

Top-Down Processing

-When your expectations affect perception

-Involves your past experiences, knowledge, motivations and cultural background in perceiving the world

-Higher mental functioning influences how you understand objects and events

-Conceptually-driven or hypothesis driven

-Ex: droodles Ponce the drawing is identified, you can see and find meaning in them)

Phonemic Restoration

-a perceptual phenomenon where under certain conditions, sounds actually missing from a speech signal can be hallucinated by the brain and clearly heard

-i.e. your friend says “-og” at a party and your top-down processes allow you to understand that she said dog without hearing the ‘d’

Object Identification

-A constructive, interpretative process

-The ability to perceive an object’s physical properties Psuch as shape, color and texture) and apply semantic attributes to the object, which includes the understanding of its use, previous experience with the object and how it relates to others

Geons

-Geometrical Ions

-the simple 2D or 3D forms such as cylinders, bricks, wedges, cones, circles and rectangles corresponding to the simple parts of an object in Biederman’s Recognition-by-components theory. The theory proposes that the visual input is matched against structural representations of objects in the brain.

Influence of Contexts and Expectations

-From the context you are in, you generate expectations about what objects you are and are not likely to see nearby

Set

-Temporary readiness to perceive or react to a stimulus in a particular way -Motor, mental or perceptual

Motor Set

-A readiness to make a quick, prepared response

Mental Set

-A readiness to deal with a situation, such as problem solving or a game, with learned rules, instructions, and expectations

Perceptual Set

-A readiness to detect a particular stimulus in a given context