Stimulus Sensation Perception

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Stimulus

• A stimulus is any input from the environment that affects one or more of the senses. It can be:

  • External: such as light, sound, smell, taste, or touch.

  • Internal: such as a pain or hunger signal.

• Stimuli are the starting point for sensation and perception, providing the raw information our brains use to create our experiences of the world.

Sensation

• Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. This involves:

  1. Reception: The stimulation of sensory receptors by energy (e.g., light, sound, heat) or chemicals (e.g., molecules of odor or taste).

  2. Transduction: The conversion of this energy into neural impulses. For example, the eye transduces light into electrical signals.

  3. Transmission: The delivery of these neural impulses to the brain for further processing.

• Sensation is a bottom-up process, meaning it starts with the sensory input and works its way up to the brain.

Perception

• Perception is the process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. It involves:

  • Organization: The integration of sensory inputs to form a coherent representation.

  • Interpretation: Attaching meaning to the sensory information based on our experiences, expectations, and context.

• Perception is a top-down process, meaning it uses prior knowledge and expectations to interpret sensory information.

Detailed Explanation of the Concepts

1. Stimulus:

   • A stimulus can be measured in terms of its:

     • Intensity: How strong or weak the stimulus is. For example, the brightness of a light or the loudness of a sound.

     • Duration: How long the stimulus lasts.

     • Frequency: How often the stimulus occurs (relevant for stimuli like sound waves).

   • Different types of stimuli activate different types of sensory receptors:

     • Photoreceptors: Respond to light (vision).

     • Mechanoreceptors: Respond to mechanical pressure or distortion (touch, hearing).

     • Chemoreceptors: Respond to chemical stimuli (taste, smell).

     • Thermoreceptors: Respond to temperature changes.

     • Nociceptors: Respond to painful stimuli.

2. Sensation:

   • Sensory thresholds are important in sensation:

     • Absolute threshold: The minimum stimulation needed to detect a particular stimulus 50% of the time.

     • Difference threshold (just noticeable difference - JND): The minimum difference between two stimuli required for detection 50% of the time. This is related to Weber's Law, which states that the JND is a constant proportion of the original stimulus intensity.

     • \frac{\Delta I}{I} = k , where \Delta I is the increment threshold, I is the initial stimulus intensity, and k is the Weber fraction.

   • Sensory adaptation: Diminished sensitivity as a consequence of constant stimulation. For example, you eventually stop noticing a persistent odor in a room.

3. Perception:

   • Perception is influenced by a variety of factors, including:

     • Attention: Selective attention focuses awareness on a limited aspect of all that we are capable of experiencing.

     • Perceptual set: A mental predisposition to perceive one thing and not another. This is influenced by our experiences, assumptions, and expectations.

     • Context: The surrounding environment and situation can influence how we perceive stimuli.

   • Gestalt principles of perceptual organization: These are rules that describe how we organize sensory information into meaningful forms:

     • Proximity: Grouping nearby figures together.

     • Similarity: Grouping figures that are similar to each other.

     • Closure: Filling in gaps to create a complete object.

     • Continuity: Perceiving continuous patterns rather than discontinuous ones.

     • Connectedness: Perceiving spots, lines, or areas as a single unit when they are connected.

   • Depth perception: The ability to see objects in three dimensions although the images that strike the retina are two-dimensional. This relies on:

     • Binocular cues: Depth cues that depend on the use of two eyes (e.g., retinal disparity, convergence).

     • Monocular cues: Depth cues available to either eye alone (e.g., relative size, interposition, linear perspective).

   • Perceptual constancies: Perceiving objects as unchanging (having consistent shapes, size, lightness, and color) even as illumination and retinal images change.