4.13. Key Terms

The minimum value of a stimulus required to activate a given sensory system.

The absolute threshold is the lowest level of stimulus intensity that a person can detect. For example, if you add sugar to a glass of water, there is a point at which the sweetness becomes noticeable. Below that point, the sweetness is undetectable. This threshold varies across individuals and can change based on conditions or levels of training.

Consider a dimly lit room. You might not notice a small amount of light coming from a candle until it reaches a certain brightness—this brightness is your absolute threshold for detecting light in that environment.

Depth perception cues that require both eyes to interpret the distance and depth of objects.

Binocular cues are important for our depth perception. They involve visual information from both eyes, which creates slightly different images based on the distance of objects from us. The brain uses the disparity between these images to judge distance. The greater the disparity, the closer the object appears.

When you look at a friend standing close to you and then one who is further away, your eyes angle inward to focus. The closer your friend is, the more your eyes converge. This convergence gives you a cue about how far away they are.

A recognition process that begins with the sensory input, where perception starts from the individual pieces and builds up to the whole.

Bottom-up processing refers to a way of understanding information that begins with the raw sensory data. For instance, when you see a complete object, you first recognize its individual features (like its color, shape, and texture) and then combine these features to understand what the object is.

Imagine assembling a puzzle. You start with individual pieces (colors, patterns) and gradually see how they fit together to form a complete picture.

The ability to perceive the world in three dimensions and judge the distance of objects.

Depth perception allows us to gauge how far away objects are. This involves a combination of binocular cues (using both eyes) and monocular cues (using one eye). These cues help us interpret the spatial arrangement of our visual world.

When driving, you need to judge how far an oncoming car is from you. Your brain uses depth perception to assess whether you have enough time to make a turn safely.

The minimum difference in stimulus intensity required to notice a difference between two stimuli.

The difference threshold, also known as the just noticeable difference (JND), refers to the smallest change in stimulus that can be detected. This threshold also varies among individuals and situations, often tested through repeated trials to establish how much change is needed before people notice.

Think about adjusting the volume on your music player. If you increase the volume slightly, at one point you may not notice the change. The smallest increment where you can perceive a difference is your difference threshold.

The ability to focus on more than one task or stimuli at the same time.

Divided attention refers to the process of distributing your focus between multiple stimuli or tasks. This is often easier when the tasks are highly practiced and automatic. The effectiveness of divided attention can vary based on the complexity of the tasks involved.

Multitasking is a common experience. For example, when talking on the phone while cooking, you might be able to manage both tasks competently if you've practiced them both enough.

The perceptual tendency to organize sensory input into a figure (the focus of attention) and a ground (the background).

Figure-ground segregation is a fundamental aspect of perception where we distinguish an object (the figure) from its background (the ground). The mind automatically assigns certain visual elements as the focal point while deeming others as part of the background.

When you read a book, the words (the figure) are what you focus on, while the white page (the background) recedes into the background, making it easier to process the text.

A theory suggesting that only certain stimuli are fully perceived while others are filtered out.

Filter theory postulates that our sensory inputs are filtered in our brains, allowing only some stimuli to pass through for deeper processing. According to this theory, this occurs at an early stage of perception, preventing overload of information.

Imagine trying to concentrate in a noisy café. While you hear multiple conversations, you manage to focus on the one with your friend, filtering out the rest.

An extension of filter theory that suggests unattended stimuli are not completely blocked but rather attenuated.

This theory suggests that while we filter out irrelevant stimuli, some unwanted signals are still processed at a lower intensity. This allows for the possibility of coming back to those signals if they become relevant.

In a crowded party, while listening to a friend, you might still hear your name mentioned in another conversation, indicating that your attention can switch if something becomes significant.

German for 'form' or 'shape'; in psychology, it refers to the idea that our perception is a whole that is greater than the sum of its parts.

Gestalt psychology emphasizes that humans perceive entire patterns or configurations, not just individual components. This shows that our perception tends to be organized and structured, leading to interpretations that can differ significantly based on context.

Consider a musical band—if you only listen to each instrument separately, you get a different impression than when you hear them together as a complete piece. The whole song has more meaning than the sum of its individual notes.

Depth cues that require only one eye to interpret distance and depth.

Monocular cues allow us to perceive depth and distance with one eye. These cues include interposition, relative size, and linear perspective, which give us information about the spatial arrangement of objects.

When driving, you may notice that the lines on the road seem to converge as they stretch away into the distance. This is a monocular cue helping you understand how far away the horizon is.

The ability to perceive objects as stable and unchanging despite changes in sensory input.

Perceptual constancies allow us to recognize familiar objects under various conditions, enabling us to see them as stable in shape, size, and color. This helps in maintaining a consistent perception of our environment.

Think of seeing a door as a rectangle regardless of whether it's open or closed. Even if the shape changes visually, you still recognize it as the same object due to shape constancy.

An optical illusion where stationary objects appear to move when presented in succession at a specific rate.

The phi-phenomenon occurs when our eyes perceive a series of images presented in quick succession as continuous motion. This is a crucial element in how we perceive movement in film and animation.

When watching a flipbook, each individual image is static, but when flipped quickly, they appear as if they’re moving. This is the phi-phenomenon in action within our visual system.

The process of focusing on specific stimuli while ignoring others.

Selective attention is vital for managing the overwhelming amount of information our senses receive. It enables us to focus on what matters most in our immediate environment while filtering out unrelated distractions.

Think of being at a concert where multiple noises occur. You can tune into the music despite chatter around you, focusing on what you deem most important or enjoyable.

The ability to maintain attention on a specific stimulus for an extended period.

Sustained attention, also known as vigilance, refers to how well we can concentrate over longer durations. This is essential in activities where constant focus is needed, such as monitoring tasks in air traffic control.

Imagine you're studying for an exam. You need to keep focus for hours on the material without getting distracted or losing attention. This is your sustained attention at work.

A recognition process that begins with the brain interpreting the context of whole objects before analyzing individual components.

Top-down processing uses prior knowledge, experiences, and expectations to understand stimuli. It contrasts with bottom-up processing by starting with the bigger picture rather than the details.

Think of how you can read jumbled words like 'Ths si a tset'. You can comprehend the sentence because your brain uses context and knowledge of language to fill in the gaps.

Misperceptions that occur when the mind interprets sensory information incorrectly, resulting in a mismatch between perception and reality.

Visual illusions arise when the brain receives information that it interprets inaccurately, leading to distorted perceptions. These experiences highlight the complexity of visual perception, as our brains construct our view of reality.

Consider the classic optical illusion of the Müller-Lyer line, where two lines of equal length appear different due to the attached arrows at their ends. This shows how perception can trick us.

--