Lecture 12 - Spatial Vision

Lancaster University Sensation and Perception: Spatial Vision

Introduction to Spatial Vision

Definition: The ability to perceive and interpret spatial relationships in the environment, allowing individuals to navigate and engage with their surroundings effectively.

Functions:

  • Navigation: Essential for orienting oneself in complex environments, such as urban settings or while driving.

  • Object Recognition: Critical for identifying and distinguishing objects based on their spatial layout and features.

  • Daily Tasks: Plays a vital role in activities like reading, where the brain integrates visual information to decode text, and driving, where spatial awareness is crucial for safety.

Spatial Frequency

Concept: A measure of detail present in visual stimuli, defined in cycles per degree of visual angle, influencing how we perceive fine details versus broader forms.

Types of Spatial Frequency:

  • High Spatial Frequency: Responsible for detecting fine details; crucial in activities requiring precision such as reading small text or seeing facial expressions.

  • Low Spatial Frequency: Captures broader shapes and forms, often perceived in landscapes or when observing large objects.

  • Example Frequencies:

  • 1.5 cycles/degree (broad detail)

  • 4 cycles/degree

  • 7 cycles/degree

  • 9.5 cycles/degree

Contrast Sensitivity

Definition: The ability to detect differences in luminance (lightness and darkness), which is fundamental to recognizing shapes and patterns in visual environments.

Importance:

  • Object Detection: Vital for determining the boundaries of objects and identifying them against various backgrounds.

  • Measurement Methods: Demonstrated through experiments comparing high vs. low contrast conditions, showcasing individual differences in detection abilities.

    • Individual Thresholds:

    • Low Threshold: Indicates high sensitivity, meaning an individual can see objects at lower contrast levels.

    • High Threshold: Indicates low sensitivity, requiring higher contrast for visualization.

Contrast Sensitivity Function (CSF)

Study: Investigated contrast sensitivity across different species, including cats, birds, and humans.

Findings: Cats exhibit greater sensitivity to lower spatial frequencies, enhancing their ability to detect motion, while raptors show sensitivity to higher frequencies crucial for spotting prey.

Fourier Analysis

Concept: Visual processing involves distinct channels that are specialized for different spatial frequencies and orientations, allowing the brain to analyze complex images.

Oblique Effect

oblique effect = The oblique effect refers to the phenomenon whereby human sensitivity to visual stimuli is not uniform across different orientations. Specifically, individuals show greater sensitivity to horizontal (0°) and vertical (90°) orientations compared to diagonal orientations.

Research: Campbell et al. (1966) identified differential sensitivity to orientation in spatial stimuli.

Findings: Humans are most sensitive to horizontal (0°) and vertical (90°) orientations over diagonal angles, which has implications for how we design visual displays and environments.

Real World Orientations

Study by Coppola et al. (1998): Anayzed the prevalence of different orientations in diverse environments (e.g., indoor, outdoor, and natural settings).

Findings: A higher prevalence of horizontal and vertical orientations exists in these environments, which may influence visual processing and adaptability.

Types of Vision

Central Vision

Characteristics:

  • Provides the highest acuity; essential for recognizing fine details in tasks like reading and facial recognition.

  • Rich in cone cells, which are responsible for color perception and detail-oriented tasks.

  • High Acuity: It provides the highest visual resolution, allowing us to seefine details, which is essential for tasks like reading, recognizing faces,and discerning colour.

  • Colour Perception: It is rich in cone cells, making it sensitive to colourand enabling colour discrimination.

  • Focused Attention: It is where we direct our gaze for tasks requiringprecise focus, as this area provides the sharpest, most detailed view

Parafoveal Vision

Functionality:

  • Supports reading and information scanning, allowing slight shifts of focus while retaining the ability to process surrounding details rapidly.

  • Supporting Reading and Scanning: It helps in processing informationslightly off-center, which aids in activities like reading by providing apreview of nearby words. This allows us to move our eyes moreefficiently across lines of text.

  • Peripheral Preview for Focus Shift: It also gives hints about what is inthe near periphery, enabling quick, accurate shifts in focus, such aswhen we are scanning a room.

Peripheral Vision

Advantages:

  • Detecting Motion: It is highly sensitive to motion, which helps usdetect movement in the environment. This is an evolutionaryadvantage for detecting threats or changes in our surroundings.

  • Spatial Awareness: It contributes to spatial orientation by via opticflow, allowing us to navigate our environment and maintain balance.

  • Low Light Sensitivity: It relies more on rod photoreceptors, which are better suited for low-light conditions, giving us greater night vision nand awareness in dim environments

  • Highly sensitive to motion and changes in spatial orientation, playing a critical role in detecting threats or sudden environmental changes.

  • Primarily utilizes rod photoreceptors, which are essential for vision in low light conditions and detecting movement.

Retinal Processing

Cell Types:

  • Cones: Located primarily in the fovea, these cells provide high spatial acuity and are crucial for color vision and detail recognition.

    • one to one connections

    • primary in the fovea

    • offers high spatial acuity

  • Rods: Predominantly found in the peripheral retina, they allow for low-light vision and contribute to motion detection through signal pooling.

    • signal pooling

    • primarily in the periphery

    • offers sensitivity

Crowding in Vision

Definition: A phenomenon where visual recognition of objects is hindered by nearby cluttered elements (flankers), affecting perception especially in peripheral vision.

Studies:

  • Flankers significantly impact peripheral vision but have minimal effects on central vision performance.

  • Effective crowding is more pronounced when the distance between the target and flankers is reduced.

Developmental Dyslexia and Crowding

Findings: Individual with dyslexia experience unique challenges regarding crowding.

  • They often display reduced crowding in peripheral vision but increased crowding in central vision, leading to difficulties in text recognition.

  • Study Results: Indicate that utilizing extra-large spaced text can improve reading accuracy in dyslexic children by minimizing crowding effects.

Studies have reported that individualswith developmental dyslexia canexperience less crowding in the periphery,but more in central vision, compared tocontrols (Geiger & Lettvin, 1987; Lorussoet al. 2004)

.Bertoni et al. (2019) found that thereading accuracy of children with dyslexiais improved with extra-large spaced text.


Crowding-like mechanisms could also play a key role in numerical perception through ensemble coding when there are many objects.

Castaldi et al (2020) showed that participants with developmental dyscalculia (DD) experienced more crowding compared to controls

Peripheral Vision and Movement Detection

Functionality: Essential for detecting sudden changes in the environment, which triggers focus shifts necessary for reaction times and maintaining balance, whether stationary or during movement.

Contrast Sensitivity in the Periphery

Research Approach: Measured how well individuals can discriminate stimuli in peripheral vision using sine wave vertical bars to assess visual performance.Method: Two-alternative forced choice technique; sensitivity is calculated as the reciprocal of the threshold.