Untitled Flashcards Set

Perception

Integration of sensory impressions in the external world. The brain constructs what we take to be a reality

Perception applies nonconsciously. These processes are immediate.

Cognitive tends to be conscious. This process takes time.

Perception is the automatic process of detecting and interpreting sensory input from the environment (e.g., sights, sounds, smells.)

Cognition involves higher-level mental processes that interpret, analyze, store, and use the information gathered through perception.

Behaviors that require conscious actions can come only from the nonconscious (An example would be thinking of a cow. Thinking about the cow is conscious, however, the color, how far the cow is (distal stimulus, the distance, or prox stimulus, the light), and how it looks is nonconscious.

Psychophysics

The study of the relationship between physical stimuli and our perception of those stimuli. Relationship between mind and physics.

Two main questions in Psychophysics

1. How intense the stimulus has to be to detect it (Absolute Threshold)

2. How much stimulus needs to change in order for it to appear twice as intense. (Difference Threshold)

Absolute Threshold

1. Determining the detection threshold is not clear-cut due to:

• Physiological variability: Differences in individual physiology affect sensory perception.

• Psychological variability: Levels of attention, interest, and motivation can vary.

• Environmental variability: Factors such as lighting and background noise.

Defined to detect the stimulus 50% of the time or the percentage that you choose.

2. Classical Methods

1. Methods of Limits 

• Stimuli are presented in ascending or descending order to find the threshold.

2. Methods of Adjustment

• Stimuli is adjusted until participants can detect it themselves.

• It is more subjective, but often the quickest.

3. Methods of Constant Stimuli

• Randomized stimuli to prevent habitation or anticipation

• Considered the best method but is very time-consuming

Difference Threshold

1. Determining different thresholds is Weber’s Law.

JND= K x S = Weber’s Law. Or K= JND/S

JND= Just noticeable difference (perception)

K = constant to be determined (environment)

S = Given standard stimulus (environment)
ROC curves are used as a tool for optimizing detection systems.

We usually want to know what K is

If we are trying to find how long a line should be to perceive that it is longer than a standard line, there should be multiple lines to compare to the standard line, called the comparison line. If the standard line is 100cm and the comparison line is 110cm you would subtract 110-100 to get 10 cm. So 10cm = JND and 100 is S since that is the standard stimuli.

Rearrange the formula so K=10/100 = .10 = K

Another example 100g of bee bees (Standard)

I give you 10 more weights for you and you notice that it is heavier. Which = 110g (Comparison.)

Then it’s the same as what I highlighted above.

Top-Down Processing: 

A cognitive process that starts with a large conceptual framework and works down to the finer details. This involves using prior knowledge, experiences, and expectations to interpret sensory information.

Bottom-Up Processing: 

A sensory-driven approach that begins with sensory input and works upwards to form a perception. This method relies on the raw data of the sensory stimuli collected from the environment without the influence of prior experiences or expectations.

Vision

The stimulus: Electromagnetic Radiation (Light)

1. Waves vary significantly in their wavelength

We have three cones that help us see color
Varies from long RADIO to very short GAMMA waves 

1.  measured in nanometers

Wavelength is associated with color

B.  Waves vary significantly in their Wave Height

1.  Wave height referred to as amplitude

1.  Amplitude reflects the amount of energy

Amplitude is associated with perceived Brightness

C. Waves also vary in terms of their Complexity

1. A “pure” wavelength is composed of a single

regularly oscillating wave

2. A “complex” wavelength is composed of several pure wavelengths combined.

Note the “complex” green waveform represents the combination of the “pure” red and blue waveforms. Complexity is associated with perceived Saturation. 

The most complex waveform we can perceive is seen as white light. Hence, completely saturated light is seen as a pure color. - TEST QUESTION MAYBE???

Some other important terms 

1. Distal versus Proximal Stimulus

• Distal Stimulus - object in the world

• Proximal Stimulus - a projected image of an object on the retina

• Visual Angle - Refers to the size of the projected image on the retina

S1 above is closer to the eye than is S2 and so S1 produces a larger visual angle on the retina than does S2.

1. Your thumb at arms length subtends about 1 degree of visual angle

2. The farther away an object, the smaller the visual angle it subtends

IV. Duplicity Theory – now well supported idea that rods and cones mediate different visual properties

 Retina contains ~ 120 million rods and ~ 6 million cones

1. Fovea contains only cones – mediates

perception of color and details (acuity)

Visual Pathways in the Brain

• Information pathways occur post-retina:

  • Primarily through the Lateral Geniculate Nucleus (LGN) and then to the Primary Visual Cortex (PVC).

  • Two parallel pathways: Dorsal Pathway (where) and Ventral Pathway (what).

• Dorsal Pathway: Connected largely to motion and spatial location.

• Ventral Pathway: Responsible for object recognition and detail processing, associated with face recognition and color.

Blindsight and the Division of Visual Processing

• Blindsight: A condition resulting from upper or lower pathway damage leading to a disconnection in perception;

  • Patients may navigate obstacles without conscious visual processing, illustrating dissociation of perception and awareness.

• Damage to specific areas leads to phenomena like prosopagnosia (inability to recognize faces), highlighting brain modularity.

Visual Field Processing

• Each eye contributes to both visual fields; the right visual field projects onto the left side of both retinas and vice versa.

• This crossing at the Optic Chiasm allows for redundancy and complex processing in visual perception.

• The representation exists in both hemispheres, aligning with the dorsal and ventral pathways for detailed processing based on location and identity.

Research Insights from Hubel and Wiesel

• Conducted experiments on cat visual processing, notably identifying kinds of responsive cells:

  • Simple cells: Fire in response to lines with specific orientations.

  • Complex cells: Respond to moving lines and orientations.

  • Hypercomplex cells: responds to corners or lines connected to each other.

  • Cells in the visual cortex create a retinotopic map, aligning with the structure of the retinal input.

  • Their findings illustrate how the brain organizes visual information and emphasizes the role of orientation, movement, and connection.

Summary of Visual Processing

• In essence, visual perception is a complex, multi-layered process involving:

  • Sensory detection via rods and cones.

  • Multi-level processing through specific pathways leading to distinct cognitive functions.

  • Integration and analysis through specialized receptive fields in the visual cortex.

Brightness and Contrast 

Visual systems. Host have two competing issues: having a good operating range and having good contrast sensitivity. Good operating range has a cost of having good contrast sensitivity and vice versa

Us humans have many operating ranges

It’s important for us to be sensitive to lines because everything we look at are lines.

Lines and contours are fundamental components of visual perception.

Evolving Solutions in Visual Systems

3. Visual systems have evolved to use multiple operating curves.

1. Overlapping Short Ranges: By using overlapping short ranges within operating curves, visual systems can efficiently respond to significant brightness differences while maintaining good contrast sensitivity.

2. Light and Dark Adaptation: The visual system undergoes two types of adaptation—light adaptation, which increases sensitivity in bright environments, and dark adaptation, which enhances sensitivity in low-light conditions. These adaptations allow for quick adjustments to fluctuating light levels.

3. Practical Implications: This adaptability means that individuals can seamlessly adjust to different lighting environments, such as moving from sunlight to shade, maintaining effective vision and readability in varying contexts.

Gelb's Setup for Brightness Perception Demonstration

Gelb's demonstration, conducted in 1929, effectively illustrated the ratio principle of brightness perception. The setup involved a black disk placed on a surface reflecting bright light.

Key Elements of the Setup:

1. Black Disk: The primary subject in the experiment, initially perceived as black.

2. Bright Light: A bright light source was used to illuminate the disk, altering the light reflected off the disk.

3. Contrast Manipulation: As the intensity of the reflected light surrounding the black disk was changed, the disk's perceived brightness shifted dramatically.

Observations:

• The black disk began to appear white in the presence of the bright light, showcasing how surrounding light can impact the perceived color and brightness of an object.

The black disk turned white due to the influence of the lantern’s bright light. As the intensity of the reflected light surrounding the disk increased, it altered the perceived brightness of the disk. The brain interprets colors and brightness relative to surrounding conditions; therefore, with enough bright light illuminating the black disk, it appeared white. This demonstrates the ratio principle. The reason is that the brain calculates the brightness of the L (1,000) based on the brightness around it (9,000). So pretend the L is the black disk. The black disk is the 1,000 and the room is 9,000. Putting the light towards the black disk flips that ratio so that the black disk is 9000 turning it white.

The concept of visual illusions of grayness demonstrates how perception can be influenced by the surrounding context. In various visual setups, all gray bars can appear as different shades due to their contrast with neighboring colors or brightness levels. This phenomenon underscores the ratio principle by illustrating that brightness perception is relative rather than absolute. The brain interprets the perceived brightness of an area in conjunction with the brightness of adjacent areas (the gray is in the dark bar, while the other gray is in the white bar), leading to the illusion that the bars are not uniform despite having the same actual intensity. Understanding this principle helps to explain many common visual illusions and enhances our comprehension of how the visual system processes contrast and brightness.

Contrast Perception

• Contrast Perception: It's how we see differences in brightness between objects. This ability helps us tell one object from another.

• Edges and Borders: Our eyes are better at spotting differences where two colors or brightness levels meet, known as object borders.

• Mach Bands: At these borders, our vision exaggerates brightness differences, creating effects called Mach bands. These bands help us see gradients of light more clearly. They exist in the proximal stimulus

• Lateral Inhibition: Retinal mechanisms that enhance contrast at the edges of objects, highlighting differences in brightness. Uses Horizontal and Amacrine cells (These ones connect to each other in the diagram of rods and codes)

• Everyday Example: When looking at a light grey disc against a darker background, we can see the edges more clearly because our eyes enhance the differences in brightness.

MACH Bands:

• Defined as the illusion of light and dark bands created near edges due to lateral inhibition.

• True/False Questions:

  • MACH bands exist in the distal stimulus? False

  • They are created by the retina's lateral inhibition? True

  • MACH bands enhance our ability to see edges? True

Nystagmus and its Role in Visual Attention

• Nystagmus: A form of involuntary eye movement that plays a crucial role in maintaining the ability to perceive edges under sustained gazes; helps prevent the fading of visual stimuli by moving the image across the retina constantly.

• Stabilized Image Experiment: Discussion of experiments demonstrating how a stable image projected onto a retina, without natural retinal motion caused by nystagmus, leads to total loss of visual perception of that image; the image effectively disappears.

 Contours and Visual Perception

• Contours Defined: Contours are technical terms for the lines that define an object's shape.

• Importance of Motion Perception: The visual system must differentiate between foreground and background to identify objects and their distances from one another.

Mechanisms of Visual Perception

• Separation of Objects: As a viewer moves, their image sweeps across the retina, necessitating motion perception to maintain awareness of separate objects in their environment.

• Edge Enhancement Mechanism: The visual system has adapted to enhance edges through a process known as lateral inhibition, which aids in distinguishing one object from another by creating illusions like MACH bands.