The way we sense (detect information from the environment through the nervous system) and perceive (organize and interpret that information in the brain) is shaped by three types of factors: psychological, sociocultural, and biological.

Sensory processing begins when specialized receptors detect environmental stimuli. The brain then interprets the resulting signals to create meaning. What you ultimately experience reflects a blend of psychological, social, and biological influences. Although sensation and perception are different processes, they happen together in real time, which is why they can be hard to separate in everyday life.

Sensation

Detection of stimuli
Sensory receptors detect physical energy specific to each sense (light waves for vision, sound waves for hearing, and so on). 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. These impulses travel through sensory neurons to the brain.

Sensory pathways

• Each sense uses dedicated neural routes to reach the brain (for example, the optic nerve carries visual signals to the occipital lobe).

Thresholds

• Absolute threshold: The minimum intensity needed to detect a stimulus 50% of the time.
• Difference threshold (just noticeable difference): The smallest detectable difference between two stimuli, described by Weber’s Law.

Adaptation

• Sensory adaptation happens when receptors become less responsive to a constant stimulus (for example, you stop noticing a strong odor after a while).

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. They help explain why some signals are easy to notice while others are missed. 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 more strongly.

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:

$$\frac{\Delta I}{I}=k$$

Where:

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

This means that as the starting (baseline) intensity increases, the change needed to notice a difference also increases. Weber’s Law applies in many everyday situations, but it may not hold at extremely low or extremely high levels of stimulation.

Perception

Perception is the process of assigning meaning to sensory signals. External factors (such as lighting or background noise) and internal factors (including attention, past experiences, and expectations) strongly influence what you notice and how you interpret it.