Sensation and perception

From physical stimulation to meaningful experience

Light, pressure variations and chemical molecules are not themselves experienced colours, sounds or smells. Receptors convert selected stimuli into cellular activity through sensory transduction. Neural systems then organise and interpret signals into perception. Separating these connected processes helps locate a problem in input quality, transmission or interpretation. An image reaching the eyes does not ensure that every object receives attention. OpenStax Psychology: sensation versus perception

Bottom-up processing depends on current input; top-down processing draws on goals, experience and expectations. Familiar text may remain understandable when letters are missing, whereas comparable omissions in an unfamiliar language can severely impair recognition. Experience therefore improves efficiency but can also substitute expectations for details actually presented. Perception is neither arbitrary imagination nor mechanical copying. It remains constrained by input while incorporating internal processing. An illusion demonstrates a feature of that interaction, not that all observation is useless. OpenStax Psychology: sensation versus perception

Thresholds describe probability rather than an absolute switch

An absolute threshold is often defined as the intensity detected on half the trials under specified conditions, highlighting variability rather than a perfectly sharp boundary. A difference threshold concerns the change required to distinguish stimuli. Weber’s law describes an approximately proportional relationship to baseline intensity within certain ranges, not an exact rule for every sense and intensity. OpenStax Psychology: sensation versus perception

Detection also depends on the response criterion. A night worker worried about missing an alarm may report ambiguous sounds as alarms more readily. Hits may increase together with false alarms. A conservative criterion can reduce false alarms while increasing misses. Sensitivity and decision criterion are distinct, so each reported detection cannot be attributed to more sensitive receptors. Researchers examine hits, misses, false alarms and correct rejections alongside noise conditions. This framework explains detection tasks but does not turn one informal home experiment into a hearing or vision diagnosis. OpenStax Psychology: sensation versus perception NYU: David Heeger, Signal Detection Theory

Vision combines cues to reconstruct space

Light passes through the eye’s optical structures to the retina. Rods and cones have different response properties, contributing to low-light vision, colour and fine discrimination. Processing begins within the retina and continues through multiple neural stages. Vision does not require a tiny observer watching a screen inside the brain; different processes support edges, motion, colour and object recognition. OpenStax Psychology: vision

Spatial perception combines binocular differences, relative size, occlusion, perspective and motion cues. Some remain available in photographs, allowing a flat image to convey depth. Carefully designed images can make otherwise useful rules generate illusions. Grouping also uses proximity, similarity, continuity and figure–ground relations. Nearby dots may appear grouped without any physical connection. In information graphics, colour and grouping influence interpretation, so visual cues should match the data relationships rather than accidentally implying a category or causal link that the evidence does not contain. OpenStax Psychology: vision; OpenStax Psychology: gestalt principles of perception

Hearing and other senses use specialised transformations

Sound waves move ear structures, and inner-ear hair cells convert mechanical events into neural signals. Frequency relates to pitch and amplitude to loudness, while spectrum, duration and auditory conditions also shape experience. Differences in arrival time and intensity between ears help locate sources; reflections alter the signals in real spaces. Difficulty communicating in noise can involve masking and attention demands rather than unwillingness to listen. OpenStax Psychology: hearing

Smell and taste respond to chemicals, while flavour also incorporates temperature, texture and olfaction. Reduced smell can make food seem bland without failure of all taste receptors. Vestibular information concerns head movement and balance, while proprioception concerns body position and movement. They cooperate with vision during standing and action. Multisensory processing is not a simple vote: reliability and context influence integration. Conflicting cues can produce discomfort or errors without proving that one sensory organ is damaged. OpenStax Psychology: the other senses

How attention affects what we notice

Attention gives some information priority and leaves other information less processed. Someone counting ball passes may miss an unexpected object, an example of inattentional blindness. Failure to notice a scene alteration can involve change blindness. Such findings show that visual input and conscious report are not in one-to-one correspondence; they do not mean that the eyes received no stimulus. OpenStax Psychology: sensation versus perception

Sensory adaptation can also make a sustained unchanging stimulus less prominent, as an initially noticeable room smell fades from awareness. Adaptation differs from shifting attention, although both may affect observation. Two accounts of the same meeting can differ because one person followed the speaker and another watched the slides, without either necessarily lying. Ask about viewpoint, task, obstruction and timing rather than comparing confidence alone. Confidence describes a subjective state but cannot independently verify that an account contains all relevant details accurately. OpenStax Psychology: sensation versus perception; OpenStax Psychology: gestalt principles of perception

Separate perceptual evidence from interpretation

In dim light, someone sees a curved object, initially identifies a snake, then discovers a cable after switching on a light. Unclear input allowed experience and threat expectations to support a rapid interpretation. Better illumination improved the evidence and changed the conclusion. This demonstrates updating rather than proving that sensation always deceives. When danger is possible, rapid imperfect responses can also carry both costs and benefits. OpenStax Psychology: sensation versus perception; OpenStax Psychology: vision

Separate noticing a curved outline, believing it is a snake and feeling afraid into stimulus features, object interpretation and emotion. Identify new evidence that could distinguish alternatives, such as shape and movement under stable illumination. Repeating the same judgement with greater confidence supplies no new information. Scientific observation similarly requires specified conditions, recorded features, alternative explanations and explicit detection criteria. Understanding constructive perception should improve checking and communication rather than deny the external world or dismiss another person’s experience. OpenStax Psychology: sensation versus perception; OpenStax Psychology: gestalt principles of perception

Bilingual terms

感觉 · Sensation

Detection and transduction of stimuli by sensory systems.

知觉 · Perception

Organisation and interpretation of sensory information.

阈限 · Threshold

A stimulus level defined by a specified detection criterion.

感觉适应 · Sensory adaptation

Changing responsiveness during sustained stimulation.

自上而下加工 · Top-down processing

Influence of experience, goals and expectations on interpretation.

Sources and further reading

• OpenStax Psychology: sensation versus perception
• OpenStax Psychology: vision
• OpenStax Psychology: hearing
• OpenStax Psychology: the other senses
• OpenStax Psychology: gestalt principles of perception
• NYU: David Heeger, Signal Detection Theory

Original course source-check record: 9 September 2026. Full Chinese and English sentence-by-sentence language review: 14 September 2026. AI editing and language review are not human clinical review. Linked institutions have not participated in or endorsed this course.