Understanding Perception

Perception

• Perception is the set of mechanisms used to recognize, organize, and give meaning to sensations from environmental stimuli
• It involves how external information perceived by our organs becomes connected within our cognitive system, making perception an active process

Sensory Receptors

• Sensory receptors capture stimulus energies and are specialized to capture only one type of specialized information
• They are sensitive to specific energy values, determining human sensitivity to certain energy levels, like the light spectrum

Primary Sensory Modalities

• Touch: Detects mechanical energy using tactile receptors in the skin, primarily the hand
• Vision: Detects electromagnetic energy using photoreceptors (cones and rods) in the eye
• Hearing: Detects sound waves using ciliated cells in the cochlea of the ear
• Taste: Detects chemical energy using taste buds on the tongue
• Smell: Detects chemical energy using olfactory receptors in the nose

Contact and Neural Response

• When energy contacts a receptor, it reacts and sends a neural message to the cortex

Psychophysics

• Psychophysics is the branch of psychology that aims to establish the general laws of sensory systems' functioning
• It tries to correlate physical magnitudes (physical world) with perceived magnitudes (cognitive world) and studies the functional dependence between body and mind and between the material and mental worlds

Founders of Psychophysics

• Ernst Heinrich Weber (1795-1878): A German anatomist and physiologist who linked stimulation intensity to the strength of sensation; Weber's work on touch led to the concept of the differential threshold
• Gustav Theodor Fechner (1801-1887): A German scientist and philosopher who aimed to give the science of the spirit a scientific character using mathematics and measurement and contributed to the concept of the perceptual threshold, fundamental in perception studies

Perceptual Threshold

• The perceptual threshold is the boundary between subjective states of sensation

Absolute Threshold

• The absolute threshold (or detection threshold) is the moment a person can perceive a stimulus
• It is the smallest intensity of a stimulation that allows statistical recognition of a stimulus in a sensory modality.
• For each sensory system, there is a lower (absolute threshold) and upper limit, meaning sensory systems are more sensitive as the detection threshold decreases
• Individuals have different basic absolute thresholds and it is determined by the stimulus intensity, where the individual indicates whether something was perceived or not with a variance of yes responses between 0 and 100%
• The perceptual threshold corresponds to the stimulus value that yields 50% "yes" responses, representing the information value with a 50% chance of being perceived.
• When below the perceptual threshold, the value is subliminal
• The function that relates stimulus values to detection percentage is the psychometric function.

Soto et al. (2008) Study

• Objective: Determine the maximum positional difference between sound and image that a viewer considers coherent in audiovisual productions
• Participants: 10 Chilean students
• Material: Video sequences + sound sequences presented through a loudspeaker, and sense, length, and emotional valence of controlled phrases
• Procedure: Presentation of an image with a person on it and then presentation of a phrase, the constant method involves varying the image's position without moving the sound position utilizing 13 adjustments in steps of 2, each adjustment was presented 9 times (234 trials)
• Measure: Percentage of "incoherent" responses for each position represented on a graph and the dependent variable (DV) was the percentage of incoherent responses for each proposition.

Differential Threshold

• It measures the limit of the difference between two stimuli below which an individual can no longer distinguish them.
• The differential threshold is the smallest difference in intensity needed for two stimuli to be differentiated
• Involves presenting two stimuli of close intensity and seeing if the difference is noticed, the reference stimulus being called the standard stimulus.
• Involves choosing a standard stimulus with a reference intensity and test stimuli with intensities either smaller or greater than the standard stimulus

Discriminating Stimuli

• The Discrimination of two stimuli in 50% of cases, subject must determine if the compared stimulus is more or less intense than the standard.
• A vertical rod measures 30 cm, is placed 3 meters away from the observer and a second vertical rod called the test stimulus is placed on the same line is 3 meters from the standard
• The variations happen on the testing stimuli, where there are the sizes 20, 25, 27, 30, 33, 35, or 40cm tests are presented randomly five times each, and on each trial, the size of the test stimulus is varied, where the observer has to say if the test looks smaller, bigger or equal to the standard the process is called a Constant Method.

Threshold Discrimination

• A threshold discrimination of 0% leads to the inability to distinguish, and a total discrimination of 100% of cases leads to completely distinguishing

Differential Threshold Formula

• The differential threshold is the difference between the upper and lower thresholds divided by 2, which is the size difference needed for the participant to differentiate the two rods.

Weber's Law

• Intensity of the stimulation affects the differential threshold
• Weber's Law states that the differential threshold (ΔI) is proportional to the magnitude of the stimulus (I): ΔI = k x I
• k is a constant specific to the sensory system
• To calculate the weight difference to feel a change: ΔI = (k x I) or ΔI = (0.05 x 300) = 15g so 15 g must be added for there to be a modification of weight sensation and calculate the differential threshold to see the difference needed to perceive an object as larger or smaller

Methods of Measuring Thresholds

• Method of Adjustment: The individual adjusts the stimulus value until it is just perceived

  • Limitation: Imprecise and coarse method for measuring thresholds, not very useful for determining an absolute threshold

• Method of Limits: The experimenter presents successive series of different stimuli, the series are alternately increasing (stimulus value increases) and decreasing (stimulus value decreases)

  • Ascending: Start with unseen stimulus and stop once the stimulus is perceived
  • Descending: Start with seen stimulus an end once there is no perception.
  • Task: Say if you perceive the stimilus each try
  • Stimulation: measurement in mm between two points of a Weber compass.
  • Person task: Say if they see (P) or don't see (NP) two points on each stimulation
  • Limits: effect of series type; the appearance of two phenomenas named -Hysteresis effect and Contrast effect.

• Method of Constant Stimuli: Presenting different stimulus levels multiple times to frame the threshold value. Stimuli are presented in a random order, subjects indicate whether the stimulus is seen or not seen. Repeated presentations determine the number of times each stimulus is perceived. Method is the most accurate and least biased for determining a perceptual threshold and establishing the psychometric function. It raises the role of observer sensitivity and manner of making decisions.

Eye Structure and Function

• The eye contains sensory and photo-receptor organs that transform light energy into nerve messages
• Light is captured by the eye and sent to transparent layers, projecting images onto the back of the retina
  • The cornea protects the lobe ocular from dust and projects light rays onto the lens, which manages the size of the captured image for near and far vision
• The lens bends and converges light
  • Light converges when far, and the lens slightly converges when near = accommodation
• The converging lens refracts light rays, which cross and project a clear image onto the back of the retina

Vision Problems

• Myopia: Overly convergent lens; image forms in front of the retina, corrected with diverging lenses
• Hypermetropia: Not enough convergence; image forms beyond the retina, corrected with convergent lenses
• Presbyopia: With age, the lens stiffens, and it cannot bend to see near; corrected with progressive lenses
• Astigmatism: Non-homogeneous transparent bodies, distorted retinal image

Retina Structure

• The retina is a membrane lining the back of the eye, containing photoreceptors that transmit light information to the brain

Retina Zones

• Fovea at the Macula:
  • Diameter: 1.5 mm, it is the shape of the eye, and it is composed of cones for day vision and color vision
• Blind Spot:
  • Lacks sensory receptors (photoreceptors), a gathering of nerve fibers forms the optic nerve to transmit nerve information to the upper center and creates a gap in the visual field

Retinal Photoreceptors

• Photoreceptors are chemically sensitive to light where a photo-pigment triggers electrical responses in photoreceptors

Types of Cone

• Cone L: reacts to a specific wave longitude - red
• Cone S: reacts to a specific wave longitude - blue
• Cone M: reacts to a specific wave longitude - green

Cones

• Nearly absent in the peripheral regions of the fovea
• Six to seven million units, sensitive to wavelength variations
• Involved in color perception (S, M, and L cones)
• Present in the fovea's central zone
• Poorly sensitive to light

Rods

• 120 million units, they are located in the retina's periphery
• Not sensitive to color except grades of gray
• Sensitive to light, are responsible for twilight vision and peripheral vision

Integration

• Cones and rods attach to bipolar cells, then to ganglion cells
• Ganglion cell axons form the optic nerve.
  • The role of formation in the optic nerve involves traits or primitive visual elements.
• Traits: The entire set of elementary sensorial represents a specific mode that allows the formation of detailed representations involving color, movement, contrast, spatial frequency.

Ganglion Cell Types

• Parvocellular Cells (P):

  • Small in size, linked to cones, they are sensitive to color and are located on the fovea level

• Magnocellular Cells (M):

  • Big in size, related to rods, and spread through the entire retina

Signals Pathways

• The nerve fiber’s axons from ganglion cells connects to the eye, from here there are 2 options

Neuronal Pathway 1

• A first group that gathers 10% of nerve fibers that are connected to the upper colliculus (tectopulvinarien system) is where one can find the M ganglion, which plays a role on reflex saccade movement.

Neuronal Pathway 2

• A second group that gathers that is 90% connected cells to to the lateral geniculate bodies. Striated Area, connects to V1 and all extra-striated areas. This is all related to air occipital

Brain areas

• V1: Treats the characteristics separately:
  • Neurons V1: oriented to orientation,
  • V4: related to color
  • V5: related to movement
  • V3: related to shape.
• Simultaneous and fast extractions occurs for every primitive Treisman & Gelade, 1980
  • The bottom-up: is environmental and stimulation based
  • Top-down: is information guided by someone's semantic memory

Contrast

• Regarding image capture being not clear. The mechanisms for capturing a blurry image relies on the contrast

Harline and Ratliff (1972)

• Relationship between contour and contrast

Contrast

• A situation in which properties make a specific spot differentiate from surrounding adjacent areas
• The role of color:
  • To study the luminance contrast one presents black lines in a blank space

Calculating Luminance

• Calculates by varying contrast between white and black lines equation: c equals l max-l min divided by l min where luminance of blank grows as the dark areas contrast is elevated.

Photoreceptors and On/Off Signals

• Non-illuminated photoreceptors exhibit slower signals. Illuminated photoreceptors in motion, lead to faster signals. Surrounding areas are inhibited by cells called cells horizontal and bipolar in order to form the contours that make an area not be considered illuminated, therefore leading to a phenomena called Illusions of Contrast.

Spatial Frequency

• Measures the speed variation on a visual scene. Anime use the same method of encoding images using speed of change. There are 2 patterns :
• High: Complex detail that can have many details made of black lines
• Low: Is just mass, made of blank lines

Angry and Smile Experiment:

• By Dr. Schyns and Oliva (1999), studied the effects of Stimuli hybrids- two images can be perceived from one image
• By varying spatial frequencies the experiment was applied and results were gathered

Colour

• Exists distinct types of cone-sensitive to distinct longitude of waves. Thomas Young: Theory of trichromatic 1801 and theories for color creation.

Additional Color Theories by Hermann von Helmoltz (1821-1894)

• There is a set of combinations made of 3 colours and a existence of four color
• Colours exist on two pair receptions, red/green blue/yellow
• Colour theory by Hering: existence of 4 basic colors. Blue is opposite yellows and red is opposite green and effects are consecutive

Vision Deficiencies

• Special Case Daltonism: 3 genes determine three vision pigments. It’s located on both chromosomes X and 7. It’s an anomaly of duplication where division can lead to the loss of green, in turn, leading to Dalton's.

Animal vision

• For Vertebrates, monkeys and birds: retines are composed of cones and rods which allow them to distinguish between colours. For mammals : retinas consist of exclusively rods. For Vision in Cats : they aren’t sensible for recognising red

Gestalt Approach To Combinations of Structural Traits

• Explains Perception in organisation as a visual arrangement being composed of a coherent group
• Structural explains decomposition of components to smaller structural components and this is explored by theory of Gestalt, that aims at the study of global implications that structure the environment

Foundational Figures

• Founders: Koffka (1886-1941), Köhler (1887-1969), Wertheimer (1880-1943) and Lewin (1890-1947), who focused on school form, which meant giving form to a meaning meaning and overall, contrasting structural logic

Law of Pregnance

• This law highlights the human tendency to turn to visual configurations that force one to see structural stable shapes instead of disconnected information, and their influence on organization

Laws Of Gestalt Perception Of Shapes

• Laws Of Proximity: Where there's a joint ensemble people tend to group figures by temporal and spatial proximity rather than perceiving them far apart.
• Law Of Similarity: Similar elements are seen is to be part of the same configuration with each other in this arrangement
• Law Of Continuity: Elements tend connect in order of trajectory instead of in a burst pattern

Closing Law

• Perception propensity in order to construct configuration. Non lacunar figures that close the shape, with the person's ability to close what's seen

Destiny law

• Recurring trend and items share a common origin

Constant size

• Recognising and seeing objects in constant shapes with modifications

Illusions

• Perception's can be altered from other visual perceptions or distortions

Objective sizes

• How small or big is a certain object on the retina. Images can be altered to fit and create constancy for size

Context Clues

• Many experiences show there a correct and proportional way to estimate sizes by the presence of perspective indicators, due the absents of perspectives objects can appear the wrong size

Constancy Perceptive Of Shape

• Entails seeing different portions and angles when the individual is Reconnaissance

• The same shapes persist in our vision system, but retinal alterations make us change the sizes

• The same way that shape constancy exist, so does the opposite is possible

Dimension

• Is really important because perception needs not just size but also to be available in order to capture objects
• The system sees a 2 dimension object and through this system it operates changes to see and perceive the three dimensions
• Body and the ability to accommodate and converge is import in human physiology

Human Adaptation

• Allows the system to make adjustments on the muscles for them to see clearly independently of distance

• Convergence is a function where, when focusing on a really close range, the viewer is obligate to see on conjunction in order for the image to be projected

• The more the object is near and focused and the system has a high convergence in what it will look at

• Soliciation on body lead to lead muscle movement: that in time leads to proprioception that in turn leads what separates the viewer from what's being watched at

• Body movement doesn't happen on distances greater tan 2 to 3 m.

• Construction through deepness:

  • Through an object that's hidding another
  • Air perspective
  • Light intensity + Objects close enough

• Line convergence helps far away objects

Perceptive View

• It relies on the amount if light coming to retina to determine what light the object
• By estimation reflectance and object can be seen even if its incomplete
• Can have effects through what an the brain is interpreting and effects it being to dark or under exposed

Vision Ways

• After V1, two ways, dorsal and ventral, are taken to treat what we see

Ways of Looking(Lieury, 2008)

• Frontal Lobe:
• Orientation+saccade programming
• Parietal Lobe:
• Location and spatial analysis
• Temporal Lobe:
• Object's Identity
• Occipital Lobe:
• Cortex - sight
• Retina pathway - colliculus:
• localisation + command oculo-motors Of ocular's movements

Retina And Treatment

Way 1 :Ventral

• It relies on the par vocellular System:*
• Fovea- thalamus-geniculates bodies - V1-V5 - infero cortex 150 Ms in action
• Specialisdesin object scene visual
• Image -sharp - colour -form
• What way milner AND Foodale

Way 2: Dorsal

Is dependant on the magnoceluaar system : retina peripheres - tubercules quadri jumeaux bodies- occulo motor- V1 - MT - V5. Specialised In motion tracking

• *Milner AND Foodale

Cognitive Approach vision

• It was born in the 1950, sight = perception - action
• Senses allows to acquire vision - the world through the sight The main view has Three functions
• Sensorial level where visual are transferred - characteristics are passed on
• Perception level where the previous sensorial are compared
• Cognitif level where it recognises what has been seen. In memory and interaction with everything has been seen by people

Deficiency

• Agrosia the ability to perceive - it can be by

• *Temporal - to detect simultaneously

• *Spacial the loss of what’s parietal - *and loss of light - which brings prosopagnosie