General Psychology 1: Foundations of Visual Perception

• Lecture: General Psychology 1
• Presented by Prof. Dr. Guido Hesselmann ([email protected])
• WiSe 2024/25
• The topic is foundations of visual perception

Recap: Wilhelm Wundt (1832-1920)

• Wundt aimed to address psychological questions like perception using scientific methods.
• Wundt believed that once the soul is seen as a natural phenomenon, the experimental method must be applied to the science of the soul
• #1 Wundt's rule: Every observation must be repeatable under the same conditions to secure results.
• #2 Wundt's rule: Conditions under which a phenomenon occurs must be systematically varied.

Themes & Questions

• Perception process
• Modalities & qualities
• Inverse problem
• Probability principle of perception
• Visual system, including optical and dioptric apparatus
• Adaptation and accommodation
• Wiring in the visual system

Perception Process

• Perception helps enable action in an environment.
• Perception is described as more than a window to the world, but also a door.
• Gibson(1966): You must perceive to move, but you must also move to perceive

Modalities & Qualities

• A distinction exists between sensory modalities and qualities.
• Modalities/Systems: Basic types of sensory sensations based on sensor/receptor.
• Qualities: Various sensations within a sensory modality.
• Adequate stimulus: The stimulus for which a specific sensor/receptor has maximal sensitivity.
• Examples of Modalities:
• Visual system, which detects brightness, hue, and saturation
• Auditory system, which detects loudness and pitch
• Olfactory system, which detects odors and possible scent classes
• Gustatory system, which detects sweet, sour, salty, bitter, and umami
• Skin senses, which detects pressure, temperature, and vibration
• Vestibular system, which detects gravity and acceleration
• Proprioceptive system, which detects the sense of force, movement and position
• Interoceptive system, which detects internal states such as blood pressure of internal organs
• Nociceptive system, which detects pain caused by tissue damage

Definitions

• Distal stimulus: The physically real object in the external world.
• Proximal stimulus: The representation of the stimulus on the receptor level.
• Sensation: Elementary mental representation of a stimulus, such as isolated stimulation of receptors.
• Perception: Complex mental representation of stimulus, organization and interpretation of complex stimuli.
• Representation: State of a cognitive/neural system corresponding to the state of the external environment

Limits of Perception

• Perception is limited by the properties of receptors and can only process certain stimuli
• All modalities are subject to limitations in stimulus intake and processing.
• The visual system can perceive light with wavelengths of approximately 400-700 nanometers.
• Technology can extend the boundaries of perception, making it possible to learn new senses.

Inverse Problem

• Reconstructing the distal stimulus from the proximal stimulus forms an inverse problem.
• Problem: A proximal stimulus can come from many distal stimuli and is thus an underdetermined problem
• Example: Different objects causing identical stimulation of the retina.

Shadows & Reconstruction

• Inverse problem: How to illustrate it?
• Observation: You see a shadow and reconstruct the object that causes it, but the solution isn't always clear.

Probability Principle

• Perception is not "true" by physical measuring standards.
• Perception constructs a relevant internal representation from available information in a selective way.
• Problem: Available info is incomplete, noisy, and ambiguous
• Probability Principle - Hermann von Helmholtz: perceiving the object that most likely caused the sensory experience.

Approaches to Investigation

• Three levels can distinguish the investigation of perception.
• #1 Physiology: Uses physics of signals and physiological basis
• #2 Psychophysics: Quantifies perception (e.g., through measurement of absolute and difference thresholds).
• #3 Cognitive Psychological Approach: cognitive influences (e.g. from prior knowledge and expectations).
• Cognitive Neuroscience: interdisciplinary investigation of neuronal fundamentals of aspects of perception

Optical & Dioptric Apparatus of the Eye

• The optical apparatus of the eye consists of the cornea, anterior and posterior chambers, iris, lens, and vitreous humor.
• Dioptric apparatus: The totality of light-refracting structures in the eye.
• Cornea contributes ~75% and the lens contributes ~25% to the refractive power of the eye.
• There is a bi-convex converging lens

Umkehrbrille

• Umkehrbrillen either invert the image seen or display it laterally inverted.
• Classical finding: After a few days, the system corrects the visual defect.
• Newer studies could not replicate these results.

Retina

• The image on the back of the retina is upside down
• There are two types of receptors: ~6 million cones and ~120 million rods.
• Fovea: The spot of sharpest vision, contains almost exclusively cones.
• There are no receptors where the optic nerve exits the retina (blind spot).

Blind Spot

• The Optic nerve must go through the existing retina to get to the brain, thereby blocking this location from having receptors
• Thus the photoreceptors lie on the backside of the neural retina

"Filling-in" Phenomenon

• Regular patterns falling in the blind spot are "filled in."

Rods & Cones

• Both are receptor types with 6 million cones and 120 million rods
• Cones provide higher resolution, while rods provide more sensitivity to light.
• Types of cones use 3 different absorption spectrums: S, M, L
• Detailed sensitivity results from different neural circuits.
• Chart of comparison:
• Number: 6 million cones Vs. 120 million rods
• Location in Retina: Cones in the center, rods in the periphery.
• Twilight Sensitivity: Cones are low, rods are high.
• Color Sensitivity: Cones are yes, rods are no.
• Detail Sensitivity: Cones are yes, rods are no.

Wiring

• Information of approx. 126million receptors are wired to the 1.2million ganglion of the retina
• Rods: higher convergence
• Fovea: higher resolution, but limited light sensitivity

Dark Adaptation

• Adaptation is the adjustment of sensory performance to constant environmental conditions.
• Constant odors lead to a reduced sense of smell.
• Dark adaptation: Increasing light sensitivity shows a kink in the curve.
• Kohlrausch kink: Sensitivity of cones dominates first, then rods

Accommodation

• Accommodation: Adapting the curvature of the lens, so objects can be seen sharply at different distances.
• Lens bands: Suspension Fibers at lens & muscle: "relaxed" lens: strongly curved.
• Remote Accommodation: ciliary muscle relaxed ---> lens straps tightened -- Lens taught-- Big focal length (f) and low refractive power (D).
• Near accommodation: ciliary muscle tense---> Lens band unfastened-- Lens bulged-- Low focal length (f) and high refractive power (D).

Near Point

• Near point: The distance from the eye below which the lens can no longer accommodate to focus on nearby objects.
• The near point is the shortest distance at which the eye can still see sharply.
• Presbyopia: The remoteness of the near point increases with age
• If the near point moves out of comfortable reading distance, corrective lenses can help

Teaser: Psychophysics

• Quantifies the relationship between physical stimulation and the strength of sensory perception
• Classical psychophysics uses methods to set physical stimuli in quantitative relationship.
• Signal Detection Theory accounts for sensory processes and decision-making.

Teaser: Psychophysical Laws

• Weber's Law: The difference threshold is proportional to the intensity of the original stimulus.
• Weber’s law: ∆S = JND = k * S, where k denotes the Weber constant
• Weber-Fechner Law: Connection between stimulus intensity and sensation intensity. (Caveat: Usually for middle stimulus).
• E = c * ln(S); Sensation is proportional to the natural Log of Stimulus. (c = Fechner’s Constant)

Material I & II

• Provides links to complete lectures on perception and visual systems

Questions for Self-Checking

• Briefly describe the concept of distal vs. proximal stimulus.
• Name two modalities and their qualities.
• Name two approaches in researching perception.
• What does the Kohlraush-kink describe and what is the foundation?
• What does one call the need to adjust lens curvature to see an object in the distance clearly?
• These questions are not typical of exam questions.

Outlook

• Visual Perception: Receptive field & brightness.
• Followed by an image with notes

Excursion: Nearsightedness (Myopia)

• Myopia: Form of visual impairment in which distant objects appear blurry.
• Far point: Distance at which object is focused; >Far point = blurry
• Axial myopia: Eyeball is too long; refractive: Light refraction through lens/cornea is too strong.
• (Axis-) Myopia starts in elementary school and progresses to adulthood.
• Risk factors: Lack of daylight & frequent close-up vision (e.g. smartphone use).
• Germany: ~15% of children nearsighted, ~45% of 25-year-olds; global increase in myopia.
• Holden et al. (2016) & WHO: ~50% of the world population will be affected by 2050.

Blindness

• People with night blindness (nyctalopia) see poorly at night or in dimly lit environments.
• Night myopia: Light rays are more strongly refracted at the pupil margin.
• Gray star or Cataract, Retinopathia pigmentosa, or Usher-Syndrome.
• Vitamin A deficiency