Perception I

Perception I: Cognitive Psychology PS21820

Lecture Information

  • Date: 31st October 2025

  • Instructor: Dr. Ioana Mihai

  • Contact Information: iom7@aber.ac.uk

  • Office Location: Room 1.29, P5

Today's Lecture Topics

  • Perception as a Process

  • Visual Perception: Visual Systems

  • The Visual Brain

  • Disorders: Blindsight

  • Object Recognition: Cognitive Theories and Processes

Definition of Perception

  • Perception: A complex series of processes through which we acquire and interpret sensory information.

  • Distinction: Perception ≠ Sensation

Types of Perception

  • What is Perception?

    • Light → Object → Eye

    • Eye → Brain → Neural Signal Interpreted by the Brain

    • Summary of the process of perception and processing within the brain.

Visual Perception - Overview

  • Light Energy: Hits objects and reflects from the surrounding environment.

  • Role of Eyes: Capture reflected light.

    • Components involved:

    • Cornea

    • Pupil

    • Lens

    • Focusing of light on the retina

Visual Perception - The Visual System

  • Accommodation: The eye's ability to focus light.

  • Retina: Thin layer of neurons located at the back of the eye, receives light.

Visual Perception - From Light to Eye

  • Transduction: The transformation of light information into neurochemical signals sent to the cortex.

    • Light exposure creates changes in electricity in the cell membrane of both cones and rods, resulting in the release of neurotransmitters.

Visual Perception - From Eye to Brain

  • Cells in Retina:

    • Cones: Responsible for color vision and sharpness of vision.

    • Found primarily in fovea; fewer in the periphery.

    • Rods: Responsible for vision in dim light and night vision; no color perception.

    • More numerous than cones; predominant in the periphery.

    • Function of rods and cones: Absorb photons, change shape, trigger neurotransmitters leading to electric signals (transduction).

Visual Perception - From Eye to Brain

  • Neurotransmitter Functions: Activates neighboring cells.

  • Light energy reaches the back of the retina first and is processed in the following order:

    • Rods & Cones → Horizontal & Bipolar Cells → Amacrine Cells → Ganglion Cells

Blind Spot and Visual Pathways

  • Blind Spot: An area with no photoreceptors, where the axons of ganglion cells collect.

  • Optic Nerve: Composed of ganglion cell fibers.

  • Optic Chiasm and Tracts: Pathway for visual information to the brain.

  • Lateral Geniculate Nucleus (LGN): Relay center where visual information is processed.

Subcortical Pathways for Visual Processing

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

  • Retina-Geniculate-Striate System: Pathway from retina to visual areas via the LGN.

  • Types of Pathways:

    • Parvocellular (P) Pathways: Relate to color and details, connected to cones.

    • Magnocellular (M) Pathways: Relate to movement, connected to rods.

    • Koniocellular Pathways: Less understood.

    • Retinotopic mapping: Represents how neighboring points on the retina also correlate to neighboring points in the LGN and visual cortex.

Visual Processing in the Brain

  • Distinct Brain Areas: Approximately 30 distinct areas are involved in visual perception.

  • Early Visual Processing: Involves areas V1 and V2, characterized by distinctive cell architecture and response to specific areas of retina stimulation. Provides complex topographical maps of vision.

  • Two Main Pathways from V1 and V2:

    • P Pathway: V1 & V2 → Ventral Stream → Inferotemporal Cortex: Involved in recognizing “what.”

    • M Pathway: V1 & V2 → Dorsal Stream → Parietal Cortex: Involved in understanding “how” or “where.”

Social Perception Pathway

  • Investigated potential Third Pathway for social perception as suggested by Pitcher & Ungerleider (2021).

  • Focus on processing dynamic social cues, central role of the Superior Temporal Sulcus (STS), common in humans and macaques.

Functional Organization of Visual Processing

  • Hierarchical View: Simplistic understanding of functional organization; includes parallel and overlapping processing dynamics.

  • Information Processing: Features feedforwarding of visual inputs, recurrent top-down processes.

  • Binding Problem: Issues with how visual features are integrated into a cohesive perception.

Treisman’s Feature Integration Theory

  • Proposes how distinct features combine into coherent objects, also termed binding.

  • Search Stages:

    1. Pre-attentive Stage: Processes features in parallel, rapidly.

    2. Focused Stage: Involves serial processing, slower; focuses on binding features together.

Additional Factors in Visual Processing

  • The role of expectations and knowledge, and how eye movements impact perception.

  • Ongoing research on binding and feature integration in visual perception.

Blindsight Condition

  • A phenomenon where individuals have intact eyes but damage to the visual cortex (V1) shows performance above chance levels in visual stimuli discrimination tests without conscious awareness of perception.

  • Relevant studies: Overgaard et al. (2008), Stoerig & Cowey (2007), Ajina & Bridge (2016).

  • Some motion perception may remain intact although there is no conscious viewing ability, affected areas include prefrontal regions.

  • There's intact connectivity between the LGN and area MT/V5.

Complexity of Making Sense of the World

  • Visual perception is a seemingly effortless but highly complex process that encompasses:

    1. Pattern Recognition: Detecting 2D visual elements; involves basic features and attributes.

    • Study reference: Navon (1977): Emphasizes global over local processing.

    • Feature Detectors: Hubel and Wiesel (1979) identified two types of neurons in V1 that are key in this process.

    • Challenges include interpreting ambiguous information and reliance on top-down processes.

Gestalt Principles in Perceptual Organization

  • Presentation of environment as complex necessitates laws governing perceptual organization.

  • Law of Prägnanz and specific laws for perceptual organization: proximity, similarity, continuation, and closure.

  • Figure-ground Segmentation: Distinction of a subject from its background; intrinsic to perception.

Learning and Memory's Role

  • Examination of brain-damaged patients reveals the impact of learning and memory.

  • Addressing perceptual challenges in 2D drawings compared to reality showcases complexity in dimensional perception.

  • Additional principles include connectedness, accentuation, and common fate; however, these principles may lead to inflexible recognition processes.

Perception-Action Model in Object Recognition

  • Ventral Stream: Central in recognizing objects.

  • Emphasizes hierarchical organization and the interplay between the ventral and dorsal streams in object recognition tasks.

Spatial Frequency in Object Recognition

  • Spatial Frequency: Level of detail in visual information categorized as coarse-to-fine.

  • Neuronal differences are observed in response to frequency.

    • High frequency travels via the slower parvocellular pathway for fine processing.

    • Low frequency utilizes the faster magnocellular pathway for coarse processing.

  • Task demands demonstrate flexibility in processing central vs peripheral vision.

Computational Approach to Object Recognition

  • Marr's model introduces the complexity of visual processing across 3 stages:

    1. Primal Sketch: A 2D description dependent on viewpoint.

    2. 2½-D Sketch: Incorporates depth and orientation; also viewpoint dependent.

    3. 3D Model: Represents shape and relative position, remaining independent from viewpoint.

  • Challenges in the computational approach arise from the inherent complexity of visual information.

Recognition By Components (RBC) Theory

  • Introduced by Biederman (1987), emphasizes basic components termed “geons” that combine in numerous configurations.

  • The process includes analysis of non-accidental properties and is generally viewpoint independent.

  • The importance of top-down processing and prior expectations are considered.

Gibson’s Affordances in Object Recognition

  • Explored the significance of action in visual perception beyond mere recognition.

  • Ecological approaches affirm that individuals perceive potential uses of objects directly and automatically.

  • Supported by fMRI evidence yet poses challenges in reasoning processes and incorporates object knowledge in perception.

Top-Down Processes in Object Recognition

  • Argues that the hierarchical view of visual processing may be overly simplified.

  • Highlights the influence of both backward (top-down) and forward (bottom-up) projecting neurons to V1.

  • Knowledge's role in enhancing attention and interpretation, especially in ambiguous settings, underscores the complexity of visual processing.

Interactive-Iterative Framework

  • Elaborates on the interplay of hypotheses and expectations predicated on goals before actually viewing an object.

  • Attention directed towards visual information significantly shaped by these expectations, which further impacts bottom-up processing.

  • Validated through fMRI (Dolan et al., 1997) and eye-tracking studies.

Conclusions on Visual Perception

  • Visual perception is a multifaceted process distinct from mere sensory stimulation.

  • Involves cascade processes throughout the visual system, highlighting complexities of hierarchical processing and dynamic interactions within the brain.

  • The majority of cognitive theories focus on bottom-up grouping of visual information but acknowledge that knowledge, action, goals, and attention modulate perception significantly.