Bottom-Up vs Top-Down Processing and Gestalt Principles

• Chapter 3 focuses on Perception.

Questions to Consider

• Why do different people perceive the same stimulus differently?
• How does knowledge about the environment influence perception?
• How does the brain tune to respond best to things likely to appear?
• What is the connection between perception and action?
• Are there neurons in the visual system that help understand others' actions?

Definitions

• Sensation involves absorbing raw energy through sensory organs (e.g., light waves, sound waves).
• Transduction is the conversion of energy into neural signals.
• Attention involves concentrating mental energy to process incoming information.
• Perception is the process of selecting, organizing, and then interpreting signals.

Sensation and Perception Overview

• Energy contains information about the world though incomplete, noisy, and distorted.
• The accessory structure modifies energy.
• A receptor transduces energy into a neural response.
• The sensory nerve transmits activity to the central nervous system.
• The thalamus processes and relays the neural response.
• The neural response is relayed to specialized areas of the cortex.
• Perception of the stimulus is created.

Perception Basics

• Perception results from stimulation of the senses.
• These can change based on added information.
• The process is similar to reasoning or problem-solving.
• Perceptions occur in conjunction.
• Human perceptual processes may be unique to humans.
• Artificial forms of perception (machines) have seen limited success and unsolved problems each time.

Human Perception Information

• The human perceptual system uses 2 forms of information.
• One form is environmental energy stimulating the receptors.
• The other form is knowledge and expectations the observer brings to the situation.

Perception Theories

• Direct perception theory involves bottom-up processing.
• Bottom-up processing is where perception comes from stimuli in the environment.
• Parts are identified and put together, then recognition occurs.
• Constructive perception theory involves top-down processing.
• Top-down processing is where people actively construct perceptions using information based on expectations.

Complexity of Perception

• Bottom-up processing starts with the senses.
• Bottom-up processing involves incoming raw data.
• Energy registers on receptors in bottom-up processing.
• Top-down processing starts with the brain.
• Top-down processing requires a person's knowledge, experience, and expectations.
• Expectations influence the interpretation of identity based on contexts.

Hearing Words

• Top-down processing influences our perception of language, based on individual experience with the language.
• Speech segmentation creates the ability to tell when one word ends and another begins.
• Transitional probabilities mean knowing which sound will follow another in a word.
• Top-down theory says unconscious assumptions shape perceptions about the environment.
• Knowledge is used to inform perceptions.
• Inference is used for what we know about the world.
• The likelihood principle says that we perceive the world as "most likely" based on experiences.

Helmholtz's Unconscious Inference

• The display is usually interpreted as a blue rectangle in front of a red rectangle.
• It could be a blue rectangle and an appropriately positioned six-sided red figure.

Perceptual Organization

• The "Old" view is structuralism.
• Structuralism suggests that perception involves adding up sensations.
• The “New” view is Gestalt principles.
• The mind groups patterns according to intrinsic laws of perceptual organization in the Gestalt view.
• Structuralism suggests a number of sensations add up to create the perception of the face.

Gestalt Principles

• The principle of good continuation suggests lines are seen as following the smoothest path.
• Good continuation helps see a rope as a single strand.
• The law of pragnanz suggests every stimulus pattern is seen so the resulting structure is as simple as possible.
• The Olympic symbol is perceived as five circles instead of nine shapes due to the law of pragnanz.
• The principle of similarity suggests similar things appear grouped together.
• Color is used in this example to show pattern of dots is perceived as vertical columns.
• The principle of familiarity suggests that things are more likely to form groups if the groups are familiar or meaningful.
• The Gestalt principles say perception is determined by organizing principles, not just stimuli activating the retina.
• The role of experience is minor, compared to intrinsic principles.
• Experience can influence perception but isn't the key driver.

Regularities of the Environment

• Common physical properties of the environment exist.
• The oblique effect suggests verticals and horizontals are more easily percieved.
• The display in these 2 nature scenes, horizontal and vertical orientations are more common.
• The light-from-above assumption suggests that people assume light comes from above.
• Shadows are used to indicate distance in the light- from - above assumption.
• Semantic regularities are the functions carried out in different types of scenes.
• A scene schema suggests knowledge of what a scene contains.

Object Perception Conceptions Compared

• Top-down processing includes unconscious inference.
• Top-down processing includes environmental regularities.
• Top-down processing includes Bayesian interference.
• Bottom-up processing includes Gestalt principles.

Neurons & the Environment

• Some neurons respond best to regularly occurring things in the environment.
• Neurons tune to respond best to what we commonly experience.
• Horizontals and verticals are examples of this.
• Experience-dependent plasticity shows similar effects.
• Greeble stimuli are used in a training program to show how neurons respond based on experience.

Movement for Perception

• Movement adds complexity to perception.
• Moving around a stimulus gives more views to create accurate perceptions.

Perception and Action Interaction

• Constant coordination occurs between perceiving stimuli while also taking action toward them.
• Action is caused by 2 streams in the brain.

Perception and Action Pathways

• The what pathway determines the identity of an object.
• The ventral pathway (lower part of the brain) is the "what" pathway.
• The where pathway determines the location of an object.
• The dorsal pathway (upper part of the brain) is the "where" pathway.
• Dissociation logic can be used to understand a complex system, deducing conclusions from malfunctions.
• Damage to different brain areas causes deficits.
• A specific area is necessary for a specific function.
• The Brain Ablation method damages specific areas of otherwise-normal animal brains.
• Controlled damage allows for clear conclusions to be drawn.
• Single dissociation means one function is lost, another remains.
• An example says Monkey A has damage to the temporal lobe. It can no longer identify objects, but can still identify locations.
• "What" and "where" rely on different mechanisms but operate in combination.
• Double dissociation requires two individuals with different damage and opposite deficits.
• An example says Monkey A with temporal lobe damage has an intact "where" but impaired "what". Monkey B with parietal lobe damage has an intact "what," but impaired "where".
• The "what" and "where" streams have different mechanisms and operate independently.
• Ungerleider and Mishkin used the "what" and "where" pathways in discrimination tasks.
• Object discrimination: Pick the correct shape. Lesioning the temporal lobe makes this task difficult.
• Landmark discrimination: Pick the food well closer to the cylinder. Lesioning the parietal lobe makes this task difficult.
• Milner and Goodale described in 1995 the perception pathway.
• The perception pathway runs from the visual cortex to the temporal lobe.
• The action pathway runs from the visual cortex to the parietal lobe.
• The action pathway is also called the "how" pathway.
• Alice can't name objects, but accurately reaches for them.
• Bert can name objects but has trouble reaching for them, which is double dissociation.

Mirror Neurons

• Mirror neurons respond while a subject watches an action being performed as if the subject was performing the action.
• fMRI research has found mirror neuron system evidence in the brain.
• lacoboni (2005) found a higher rate of mirroring if the subject's intention to perform the action was greater.

Explore perception with questions on bottom-up and top-down processing. Understand how context and prior knowledge shape sensory experiences. Questions also cover Gestalt principles, such as closure and similarity, in visual organization.