Perception and Sensory Memory Processes Notes

Object Agnosia

• Patients cannot recognize shapes but can recognize the shape itself.
• Cannot recognize the same objects in different perspectives.

Bottom-Up Processing

• Physical stimuli influence perception.
• Starts from transducers and goes up the visual process.

Top-Down Processing

• Existing knowledge influences perception.

Recognition

• Ability to match a presented item with an item in memory.

Representation

• Storage and/or reconstruction of information in memory.

Grouping

• Grouping together things that look alike.

Segregation

• Separating objects that look similar.

Figure-Ground Organization

• Distinguishing objects from the background.

Law of Good Continuation

• Perceiving an object as continuous even when it's obstructed.

Law of Proximity

• Things that are close to each other are seen as part of the same group.
• Example: AJC QWE PKX

Law of Similarity

• Grouping based on size, color, or orientation similarity.

Common Region

• Dots being circled together are seen as a group.

Connectedness

• Circles connected by lines are perceived as going together.

Law of Common Fate

• Visual elements moving in the same direction are perceived as a group.

Perceptual Interpolation

• Detecting edges using V1 detectors.

Edge Perception

• Edges carry meaning; Y/Arrow indicates a corner, T indicates occlusion.
• Angles are meaningful for good continuation.

Illusory Contours

• Perceived edges or lines in the absence of physical boundaries.
• Example: Pac-Man shape forming a triangle or a 3D square.

Bottom-Up Processing (Stimulus-Driven)

• Driven by the stimulus itself.
• Example: Seeing a capital A or H.

Top-Down Processing (Experience-Based)

• Knowledge shapes perception.

Geons

• Basic units of objects.
• Recognition by components; recognizing objects by the relation of their geons.

Viewpoint Invariance

• Vantage point doesn't matter for recognition.

Template Theories

• Point-by-point comparison to a stored "average or ideal" representation.

Problems with Template Theories

• Larger demands on memory.
• Vantage point matters for recognition.
• Cannot explain novel objects.

Brain Area for Shape Representation (Color)

• V4

Location of Object Perception

• Inferotemporal (IT) area
• Complex visual processing

Fusiform Face Area (FFA)

• Differentiates faces from one another.

Occipital Face Area (OFA)

• Helps determine if something looks like a face.

Prosopagnosia

• Lack of knowledge of faces; inability to recognize faces.
• Difficulty identifying familiar faces.

The Grill-Spector Experiment

• FFA shows selective response to familiar faces.
• Visual expertise may play a role (cars, birds, experts).

Parahippocampal Place Area (PPA)

• Scene recognition.

Topographic Agnosia

• Deficit in recognizing spatial landscapes.

Extrastriate Body Area

• Body parts (not faces).

The Results of Quiroga - Grandma Cell

• Cells respond to a particular person or landmark from different angles and contexts.
• Suggests cells respond to specific landmarks or people.

The Face Inversion Effect

• Face processing breaks down when faces are upside down.
• Holistic processing is disrupted.

Object Agnosia (Definition)

• Failure to recognize objects despite being able to see them.

Prosopagnosia (Definition)

• Inability to recognize faces.

Double Dissociation

• Prosopagnosia: Can't identify faces but can understand objects.
• Object agnosia: Can't understand objects but can understand faces.

Capgras Syndrome

• "Label" recognition intact but "emotional" recognition missing.
• Able to recognize faces but not the emotions attached.

Accidental Viewpoints

• Viewing scenes from a specific vantage point can trick the perceptual system.
• Actively reconstruct and make sense of images.
• Example: Holding the Leaning Tower or the Sun.

Heterochromatic Light

• Any light source that has multiple wavelengths.
• Able to measure.

Monochromatic Light

• Only produces very specific wavelengths.
• Example: Lasers.

Spectral Reflectance

• What is absorbed and reflected by a surface.
• Determines the color of an object.

Achromatic Lightness

• Amount of light reflected by a surface.
• More reflection = whiter, less reflection = darker.

Hue (Quality)

• Rainbow.

Saturation

• How intense a color is.

Brightness

• How much light is reflected back.

Additive Color Mixing (Mixing Lights)

• Light from light sources must be on the line to be a possible color.
• Example: Yellow and blue mix to white.

Non-Spectral Hues

• Colors not seen in the rainbow.

Relative Hues

• Brown does not exist in additive color mixing.
• Sensitive to the source of light.

Pointillism

• Small dots of paint that blend together from a distance.
• Similar to additive mixing.

Subtractive Color Mixing

• Color absorbs other parts of the color spectrum and reflects light.
• Example: Colors near blue will reflect off, others are absorbed.

Subtractive Color Mixing: Blue and Yellow

• Green is not absorbed so that is the only color that is reflected.

Metamer

• Once a good color match is made, it's called a metamer.

Metameric Matching

• Different wavelengths produce the same color experience (e.g., yellow).

S Cone

• Short blue wavelength.

M Cone

• Medium yellow/green wavelength.

L Cone

• Long red wavelength.

Cone Response to 500-nm Light

• Blue cones respond weakly, green cones strongly, red cones moderately.

Univariance

• Any single cone system is colorblind; different wavelength and intensity combinations yield the same response.

The Trichromatic Theory of Color Vision

• Three cone systems in our retinae.

Hering's Model of Opponent Processes

• Red-green, blue-yellow, white-black.
• Organizing colors by pairs that do not mix (opponents).

Afterimages

• Seeing opponents of a color after staring at it.
• Afterimage disappears when looking at black light.

Hue Cancellation Experiments

• Start with yellow light and add blue to turn it into pure white.
• At some point, the light has no color (no hue).
• Opponent color combinations destroy chromaticity in light.

Color Opponent Cells

• Colors we see, not wavelengths.

Cone Opponent Cells in LGN

• M-L cones; Y-B cones; V1.

Double Opponent Cells

• Sharpen color boundaries, color patterns, but not continuous colors.

Color Processing in the Brain

• Cells in V4 respond to perceived color, not wavelengths.

Rod Monochromacy

• Individuals with only rods cannot see color.

Cone Monochromacy

• Individuals with rods and only one cone cannot experience color.

Dichromacy

• Retinas have rods and two types of cones.
• Specific deficit of colors they cannot see.
• Majority of species are dichromats.

Tritanopia

• No S cone; lack green and yellow.

Protanopia

• No L cone; lack green and red.

Deuteranopia

• No M cone; lack green and red.

Cortical Achromatopsia

• Loss of color vision due to damage to the occipital lobe.

Common Color Errors

• Brown-blue: look alike.
• Red-green: difficult to tell them apart.
• Yellow-orange: look alike.

Yellow Surfaces

• Color reflected and coded along the yellow-blue channel.

Red and Green Surfaces

• Reflect a little bit of yellow light but red and green cannot be coded by the yellow channel.

Blue Surfaces

• Blue is the opponent color of yellow so the yellow light will remove or kill the blue.
• Reflect very little light, so they look dark.

Brown Surfaces

• Don't reflect a lot of light, so they look dark.

Orange Surface

• Yellow + Red. Yellow is reflected, but red cannot be coded by the yellow channel.

Color Constancy

• Ability to perceive the color of an object despite changes in illumination.

Lightness Constancy

• Ability to perceive the relative reflectance of objects despite changes in illumination.

Color and Visual Acuity

• Cones are clustered around the fovea and are in a midget system, giving us spatial acuity.

Synesthesia

• Accidental association of two precepts.
• Stimulation of one sensory pathway leads to involuntary experiences in another.

Motion Thresholds

• Which part of the retina is seeing the motion.

Determining Object Speed

• Farther away = slower it looks.
• Stationary to us = fast moving.

Real Motion

• Motion in the world created by a continual change in the position of an object relative to the frame of reference.

Apparent Motion

• Sequence of still images.

Correspondence Problem

• How the visual system correctly perceives the overall motion of objects.
• Local information sets of hypotheses are made by each aperture.
• Overall motion direction = hypotheses shared by all apertures.

Motion Detection in the Eye

• In the retina.
• Approximate speed of a moving object at point 1 and point 2 at time 1 and time 2.

Reichardt Detectors

• Will only fire if signals are received from both neurons.
• If the delay is too long or too short, motion neurons won't respond.
• If the object moves from right to left, neurons will also not activate.

Corollary Discharge Theory

• Motor system tells the eyes to move and sends a copy to the brain.
• When the brain/eyes are stationary, the image appears on the opposite side of the retina.
• When the eyes are following an object, the object is stationary with the retina.

Saccades

• Very quick eye movements.
• Less than 15 ms; we make approximately 3 saccades each second.

Smooth Pursuit Eye Movements

• Voluntary movements used to track moving objects.
• Example: Tracking a flying eagle or a tennis ball.

Saccadic Suppression

• Reduction in visual processing during a saccade.

MT (V5)

• Sensitive to direction and speed of motion, not in terms of detail.

Akinetopsia (Motion Blindness)

• Able to tell details of objects but not sense motion.

Weigelt (2013) Results

• Confirmed that motion is coded in MT.
• Bigger activation when paying attention to motion.

Affordance

• Information in the visual world that specifies how that information can be used.
• Example: A chair has a flat surface, so we note that we can sit on it.

Optic Flow

• Movement of objects, surfaces, and edges due to perceived motion.
• How close you are to an object and how fast that distance is closing.

Gradient of Flow

• The faster you are, the more the gradient accelerates, and vice versa.

Focus of Expansion

• The point we are looking at stays still.

Lateral Intraparietal (LIP) Area

• Parietal lobe.

Medial Intraparietal (MIP) Area

• Reaching movements.
• Transforms visual information of location to objects into how we should move our arms and how much muscle is required.

Anterior (AIP) Area

• Manipulating and grasping.
• Processes shape, size, and orientation of an object and how to grab it.

Cue Approach to Depth Perception

• Visual systems recreate the 3D world using a 2D retina.

Oculomotor Cues

• Accommodation and vergence.

Accommodation (Eyes)

• Adjusting the lens of the eye to see both near and far objects.
• Lens becomes thick to see near; thin to see far.

Vergence (Eyes)

• Bringing eyes together to focus on an object.

Occlusion

• One object partially hides another.

Relative Height

• Objects closer to the horizon are seen as more distant.

Relative Size

• More distant objects appear smaller on the retina.

Familiar Size

• Judging distance based on existing knowledge of object size.

Linear Perspective

• Parallel lines converge as they recede into the distance.

Texture Gradients

• Textures become finer as they recede in the distance.

Atmospheric Perspective

• Objects in the distance appear blurred and tinged with blue.

Shadows and Shading

• Object in front of its shadow provides distance information.

Motion Parallax

• Cue from a person's motion in the environment.
• Faster-moving objects are closer; slower-moving objects are farther away.

Deletion

• Gradual occlusion of a moving object as it passes behind another.

Accretion

• Gradual reappearance of a moving object as it emerges from behind another.

Optic Flow (Motion Depth Cue)

• Relative motion of objects as a person moves forward or backward.

Stereopsis

• Sense of depth perceived from processing the comparison of two different retinal images.

Binocular Disparity

• Images on the left and right vary on certain degrees.

Three-Dimensional Movies

• Provide two different images to each lens.

Horopter

• Region in space where images fall on corresponding locations on the two retinae.
• Fixation point with zero disparity.

Corresponding Points

• If distance is the same from both eyes, the image falls on corresponding points.

Panum's Area of Fusion

• Region of small disparity around the horopter where two images can be fused.

Diplopia

• Results from images having too much disparity to lead to fusion.

Crossed Disparity

• Direction of disparity for objects in front of the horopter.

Uncrossed Disparity

• Direction of disparity for objects behind the horopter.

Stereograms

• 2D image turned into 3D when viewed at a specific angle.

Anaglyph

• Blurry pictures that can be seen clearly with filter glasses.

Size Perception

• Size-distance invariance.

Visual Angle

• The angle of an object relative to one's eye.

Size Constancy

• Perception of an object as having a fixed size despite changes in visual angle.

Ponzo Illusion

• Two objects of the same size on the retina are perceived differently based on the background.

Muller-Lyer Illusion

• Lines with arrows make one line look bigger than the other.

Ebbinghaus Illusion

• The same object can look smaller or bigger depending on surrounding objects.