Perception: it is the process wherein the obtained sensory information from a stimulus is collected, organized, and interpreted by our mind for us to experience.

Uses of Perception:

1. It makes u mobile.

2. It makes us manipulate objects.

3. It makes us decide with symbols.

4. It makes us execute plans.

Functions of Perception:

1. Attention: which incoming information is to be further processed.

2. Localization: where objects of interest are.

3. Recognition: which objects are out there

4. Abstraction: abstract critical feature of a recognized subject.

5. Perceptual Constancy: where the objects are viewed to be unchanged.

I. Attention

Screening: only a tiny portion of the incoming stream of information is relevant, and the vast majority is irrelevant, no matter the task.

Brain Processes that Involve Attention:

1. Responsible for keeping us alert.

2. Responsible for orienting processing resources to task-relevant information.

3. The executive: decides whether we want to continue attending to the information or instead switch attention to other information.

Selective Attention

A. Eye Movements

Eye Fixations: Visual scanning takes the form of brief periods during which the eyes are relatively stationary.

Saccades: Quick jumps of eye movements

B. Weapon Focus: victims of armed crimes are often able to very accurately describe what the weapon looked like, but seem to know relatively little about other aspects of the scene.

Auditory Attention: attention is multimodal, it can move within a modality or between modalities, thus attention can also be auditory.

Shadowing: we are consciously unaware of, and remember little, if anything, about nonattended information.

Selective Attending to a Stimuli

Inattention Blindness: failure to notice the existence of an unexpected item.

Change blindness is a phenomenon where individuals fail to notice significant changes in their visual environment, even when the changes are obvious. It occurs due to limitations in our attention and perception.

II. Localization

Localization: navigating our way around the often cluttered environment grasping an object

Separation of Objects

Figure and Ground: we usually see the figure as a solid stand out and the rest is a less distinct background or ground.

Grouping of Objects: we only notice one organization or object group together at a time.

Gestalt Psychology: a subfield that claims that we perceive figures and forms as whole patterns that are more than the simple sum of individual sensations, and our brain must actively build up on these whole patterns or gestalts.

Gestalt Psychology Laws of Perception

1. Proximity: objects near each other tend to be seen as a unit.

2. Similarity: objects similar to each other to be seen as part of the sea pattern.

3. Good Continuation: objects arranged in either a straight line or a smooth curve ten to be seen as a unit.

4. Closure: even when a figure has a gap, we tend to perceive it as a closed, complete figure.

5. Common Fate: when objects move in the same direction, we tend to see them as a unit.

Perceiving Distance

Depth Cues: the basis of subtle pieces of information

Binocular Cues: is limited to objects that are relatively close, requiring the use of both eyes.

Binocular Disparity: is used to refer to the difference in the views seen by each eye.

Monocular Cues: enable you to judge depth and distance with just one eye.

Monocular Cues Used to Perceive Depth:

1. Relative Size: if an image contains an array of similar objects that differ in size, we interpret the smaller objects as being farther away.

2. Interposition: if one object is positioned so that it obstructs the view of another, we perceive the overlapping object as nearer.

3. Relative Height: among similar objects, those that appear higher are perceived as being farther away.

4. Perspective: when parallel lines in a scene appear to converge in the image, they are perceived as vanishing in the distance.

5. Shading and Shadows: whenever a surface in a scene is blocked from receiving direct light, a shadow is cast.

6. Motion: nearby objects seem to move quickly in the opposite direction while more distant objects move more slowly.

Perceiving Motion

Stroboscopic Motion: produced most simply by flashing a light in the darkness and then, a few milliseconds later, flashing another light near the location of the first light.

Real Motion: movement of an object through all intermediate points in space.

→ Some aspects of real motion are coded by specific cells in the visual cortex.

→ Such single-cell recording studies have found cortical cells that are tuned to particular directions of movement.

Selective Adaption: a loss in sensitivity to motion that occurs when we view motion

III. Recognition

Recognition: the perceptual system needs to determine not only where relevant objects are in the scene, but also what they are.

Primitive Features: information from the environment that we assemble them properly to be able to recognize.

Global-to-local Processing: understanding what the scene is - followed by local processing - using knowledge about the scene to assist in identifying individual objects.

Binding Problem: how activity in different parts of the brain, corresponding to different primitives such as color and shape, are combined into a coherent perception of an object.

Illusory Conjunction: the error of mixing up features.

Feature Integration Theory: information from the visual world is pre-attentively encoded along separate dimensions and then integrated into a subsequent attentive processing stage.

Stages of Feature Integration Theory:

1. Preattentive Stage: primitive features such as shapes and color are perceived.

2. Attentive Stage: focused attention is used to properly ‘glue’ the features together

Visual Search Task: a standard experimental procedure for distinguishing primitive features from ‘glued-together’ features in which the observer’s task is to determine whether some target object is present in a cluttered display.

Dynamic Control Theory: The system rearranges itself for different tasks - as opposed to there being many subsystems for each possible task

Determining What an Object is: The object’s shape plays an important role in determining an object.

Feature Detectors in the Cortex:

1. Simple Cells: respond when the eye is exposed to a line stimulus.

2. Complex Cells: also respond to a bar or edge in a particular orientation, but it does not require that the stimulus be at a particular place within its receptive field.

3. Hypercomplex Cells: require not only that the stimulus be in a particular orientation, but also that it be of a particular length.

Relations Among Features

→ There is more to a description of a shape than just its features: The relations among features must also be specified.

→ Gestalt psychologists emphasized that ‘the whole is different from the sum of its parts.’

Recognizing Natural Objects and Top-Down Processing

Features of Natural Objects:

→ The shape features of natural objects are more complex than lines and curves, and more like simple geometric forms.

Geons / Geometrics Ions: One popular though controversial suggestion is that the features of objects include a number of geometric forms, such as cylinders, cones, blocked, and wedges.

→ A set of 36 geons is sufficient to describe the shapes of all objects that people can possibly recognize.

→ Two or three geons are sufficient to create almost 50,000 objects

The Importance of Context

Top-down Processing: driven by a person’s knowledge, experience, attention, and expectations.

Bottom-up Processing: the mind works from a stimulus and information is processed upward to picture out what the object is.

→ Studies have shown that both pictures and words are identified more quickly and remembered more accurately when they are preceded by related rather than unrelated primes.

Ambiguous Stimulus: the effects of context are particularly striking when the stimulus object is ambiguous - that is, can be perceived in more than one way.

Temporal Context: the initial perception perseverates, depending on what you see first in ambiguous stimuli.

McGurk Effect: the conflict of auditory and visual information, leads to an illusory result.

Inversion Effect: finding that faces but not objects are extremely hard to recognize when they are presented upside-down.

Disorders that Affect Perception

Agosia: the general term for such breakdowns or disorders in recognition.

Prosopagnosia: a syndrome that can arise following brain injury, in which a person is completely unable to identify faces but retains the ability to recognize objects.

Associative Agnosia: a syndrome in which patients with damage to temporal lobe regions of the cortex have difficulty recognizing objects only when they are presented visually.

Pure Alexia: loss of the ability to recognize words.

IV. Abstraction

Abstraction: the physical description of an object is a listing of all the information necessary to completely reproduce the object, and this may mean having to look at the stimuli longer.

Extract to Abstract

→ In real life, these limitations don’t usually present a problem because you don’t need all that much detail to solve the problems assigned to you by the world.

→ You only need to know enough to carry out whatever task requires you to perceive the object to begin with.

The Advantages of Abstraction: Required Storage and Processing Speed

→ It is more efficient in many respects to perceive and encode in memory an abstraction of the object rather than an exact representation of the object itself.

→ What the subjects perceived and stored in memory corresponded very strongly to what they considered themselves to be looking at.

→ Rather than perceiving, storing, and later remembering a more-or-less literal image of what they had seen, the observers abstracted the important information

Color Metamers: different physical stimuli that lead to the exact same color perception.

V. Perceptual Constancy

Perceptual Constancy: a perception of what an object is actually like rather than a perception based solely on the ‘objective’ physical information that arrives from the environment.

A. Color and Brightness Constancy

Color Constancy: being able to tell what the color actually is despite being in different illuminations.

Available Wavelengths: the perceived color of an object based on the wavelength of the light that is reflected off the object reaching your eyes.

Source Wavelengths: wavelengths provided by the source.

Reflective Characteristic: the object itself reflects some wavelengths more than others

Brightness Constancy: refers to the fact that the perceived lightness of a particular object changes very little, if at all, even when the intensity of the source, and thus the amount of light reflected off the object changes dramatically.

B. Shape Constancy: the perceived shape is constant while the retinal image changes.

C. Size Constancy: an object’s perceived size remains relatively constant no matter how far away it is.

Retinal Image Size: the closer object projects onto a larger number of photoreceptors, which cover a larger portion of the retina.

Emmert’s Experiment: the perceived size of an object increases with both the retinal size of the object and the perceived distance of the object.

D. Illusions: Your perception of something differs systematically from physical reality.

The Moon Illusion: when the moon is near the horizon, it looks as much as 50 percent larger than when it is high in the sky, even though in fact, the moon’s retinal image is a tiny bit larger when it is directly overhead because it is a little bit closer when directly overhead than when on the horizon.

The Ames Room: a room wherein the observer looks through a peephole, and although the room looks like a normal rectangular room to an observer seeing it through the peephole, it is actually shaped so that its left corner is almost twice as far away as its right corner.