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Introduction
1. CARS
2. Psych/soc
2.1 6A: Sensing the environment
2.1.1 Sensory perception
2.1.2 Signal detection and sensory adaptation
2.1.3 Psychophysics and receptors
2.1.4 Sensory pathways and sleep physiology
2.1.5 Touch/somatosensation
2.1.6 Vision
2.1.7 Hearing
2.1.8 Gustation
2.1.9 Olfactory, kinesthesia and vestibular
2.2 6B: Making sense of the environment
2.3 6C: Responding to the world
2.4 7A: Individual influences on behavior
2.5 7B: Social processes and human behavior
2.6 7C: Attitude and behavior change
2.7 8A: Self-Identity
2.8 8B: Psych/soc factors affecting interaction and perception
2.9 8C: Elements of social interaction
2.10 9A: Understanding social structure
2.11 9B: Demographic characteristics and processes
2.12 10A: Social inequality
3. Bio/biochem
4. Chem/phys
Wrapping up
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2.1.1 Sensory perception
Achievable MCAT
2. Psych/soc
2.1. 6A: Sensing the environment
Our MCAT course is in "early access"; the content on this page is a work-in-progress.

Sensory perception

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The way we sense (pick up on, through our nervous system) and perceive (process and understand these senses with our brain) is affected by three types of factors: psychological, sociocultural, and biological.

The process of detecting environmental stimuli through specialized receptors is the starting point for sensory processing. Our brains then interpret these signals to create meaning—a combined result of psychological, social, and biological influences. Although sensation and perception are distinct functions, they interweave in real time, making them difficult to differentiate in everyday life.

Sensation

Detection of stimuli
Sensory receptors pick up physical energy specific to each sense (light waves for vision, sound waves for hearing, etc.).Examples:

  • Vision: Light waves detected by photoreceptors in the retina.
  • Hearing: Sound waves detected by hair cells in the cochlea.
  • Touch: Pressure, temperature, and pain sensed by mechanoreceptors, thermoreceptors, and nociceptors.

Transduction

  • After detection, receptors convert physical signals into electrical impulses, which are sent through sensory neurons to the brain.

Sensory pathways

  • Each sense has dedicated neural routes to the brain (e.g., the optic nerve carries visual signals to the occipital lobe).

Thresholds

  • Absolute Threshold: Minimum intensity required to detect a stimulus 50% of the time.
  • Difference Threshold (Just Noticeable Difference): The smallest discernible variation between two stimuli, governed by Weber’s Law.

Adaptation

  • Sensory adaptation occurs when receptors become less responsive to persistent stimuli (e.g., ceasing to notice a strong odor over time).

Additional sensory modalities

  • Proprioception: Awareness of body position.
  • Vestibular sense: Balance and spatial orientation.
  • Nociception: Sensation of pain.
  • Thermoception: Temperature perception.

Thresholds

Sensory thresholds are the minimum intensities needed to detect or identify a stimulus, providing insight into how we perceive our environment. Types include:

  • Absolute threshold: Faintest detectable stimulus (e.g., softest sound heard in silence).
  • Recognition threshold: Point at which a stimulus can be identified (e.g., recognizing vanilla scent).
  • Differential threshold (JND): Smallest change in stimulus intensity that is perceptible.
  • Terminal threshold: Any increase beyond this intensity is not felt as stronger.

Weber’s Law

Weber’s Law states that the just-noticeable difference (JND) between two stimuli is proportional to the original intensity.

Mathematically, Weber’s Law is expressed as:

IΔI​=k

Where:

  • ΔI represents the incremental change in stimulus intensity.
  • I denotes the initial stimulus intensity.
  • k is a constant specific to the type of sensory perception.

Larger baseline intensities demand bigger changes to notice a difference. While broadly applicable, it may not hold for extremely low or high levels of stimulation.

Perception

Perception assigns meaning to the sensory signals we receive. External factors (like lighting or background noise) and internal factors (including attention, experiences, and expectations) profoundly influence what we notice and how we interpret it.

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