Perception

Lecture Overview

• Course: Perception Cognitive Psychology PS21820

• Instructor: Dr. Ioana Mihai

• Contact Information: iom7@aber.ac.uk

• Date: 28th October 2024

Key Concepts of Perception

• Definition: Perception involves a series of processes through which sensory information is acquired and interpreted.

• Distinction: Perception is not the same as sensation; it goes beyond raw sensory input.

• Steps for perception: Reality → Sensory system (eyes, ears ext.) receive information → Perception (interface between cognition and outside world) → Cognition and knowledge system/ memory.

• Always two way, we are never passive receivers of information

Visual Perception Process

• Humans are heavily visual

• Fundamental Sequence:

  • Light hits an object → Light reflected → Light captured by the eye and becomes electric signal to send to the brain → Neural signals processed by the brain.

Visual Systems

• How Light is Processed:

  • Light passes through the cornea, pupil, and lens to focus on the retina.

  • Accommodation: The adjustment of the eye's optical system to focus on images at different distances.

Anatomy of the Retina

• Structure:

  • Retina: A thin neuron layer that receives light through cones and rods

  • Key components include rods (for dim light, no colour) and cones (for colour and detail, only ones in the fovea).

Transduction in Visual Perception

• Definition: The transformation of light info into neurochemical signals that reach the cortex.

• Process:

  • Light exposure alters cell membrane potential in cones and rods, triggering a cascade of neurotransmitter release.

  • Outgoing signals activate neighbouring neurons for further processing.

Pathways of Visual Information

Subcortical Pathways

• Superior Colliculus: Responsible for eye movements and orientation reflexes.

• Retina-Geniculate-Striate System: Pathway from the retina to visual cortex via the lateral geniculate nucleus (LGN).

Brain Areas Involved

• Visual Processing Areas: Approximately 30 distinct brain areas dedicated to visual perception.

• V1 and V2: Early visual processing zones, critical for processing visual information.

Processing Pathways

• P Pathway: Ventral stream for recognizing "what" (inferotemporal cortex).

• M Pathway: Dorsal stream for determining "how" or "where" (parietal cortex).

Third pathway? https://doi.org/10.1016/j.tics.2020.11.006

Feature Integration Theory

• Developed By: Treisman (1980, 1998)

• Stages of Search:

  1. Pre-attentive Stage: Rapid parallel processing of basic features.

  2. Focused Stage: Serial processing that is slower and involves binding features together.

Binding Problem

• Complexity of Perception: Requires both bottom-up and top-down processing.

• Expectations and Eye Movements: Impact the perception process.

• How does search happen?

  1. Pre-attentive stage:

  • In parallel (all at once)

  • Basic features processed rapidly;

  2. Focused stage:

  • Serial process (one at the time)

  • Slower

  • Binding of features together

Blindsight

• V1 damage but above chance performance in forced-choice tests

• If shown two pictures and asked if they are similar or not they will say they can’t see anything, but when forced to decide they perform above average. Indicates unconscious visual processing

• No conscious visual perception, some motion potential

• Characteristics: Ability to respond to visual stimuli without conscious perception.

• Findings: Indicate reorganization in visual perception circuits following injury.

Object Recognition

Cognitive Theories and Processes

• Pattern Recognition: Integrating 2D visual elements into coherent forms.

• Gestalt Principles: Laws that explain how we organize visual stimuli, such as proximity and similarity.

Role of Learning

• Influence of Memory: Observations from brain-damaged patients show the importance of prior knowledge in object recognition.

Top-Down Processing

• Complex Interaction: Emphasizes how perception is influenced by knowledge, goals, and context.

• Interactive-Iiterative Framework: Expectations guide attention and affect perceptions of objects before visual contact.

Conclusion on Visual Perception

• Summary: Visual perception is complex, involving cascading processes in a hierarchical system. Although theories provide a framework for visual grouping, cognitive functions such as knowledge and attention play critical roles in modulating how we perceive the world.