Perception: Difference between revisions

Visual perception can be understood as a diverse process that begins with the transformation of light stimuli into meaningful cognitive interpretations involving retinal sensing through photoreceptors and cortical processing in multiple brain areas.<ref name=":0">Donato, R., Pavan, A., & Campana, G. (2020). Investigating the Interaction Between Form and Motion Processing: A Review of Basic Research and Clinical Evidence. ''Frontiers in Psychology'', ''11''. <nowiki>https://doi.org/10.3389/fpsyg.2020.566848</nowiki> </ref> The photoreceptors receive light signals through the retina, converting them into electrical signals. Those signals are then transmitted along the optic nerve in the eye in order to reach the lateral geniculate nucleus before arriving at the striate cortex. This cortex, known as the visual cortex, serves as a fundamental basis for the conscious perception of static form and local brightness differences, establishing the base for more complex visual processing.<ref>Pollen, D. A. (1999). On the Neural Correlates of Visual Perception. ''Cerebral Cortex'', ''9''(1), 4–19. <nowiki>https://doi.org/10.1093/cercor/9.1.4</nowiki> </ref> Following that, after leaving the visual cortex, signals travel along the dorsal stream to the parietal cortex, serving for spatial orientation and motor actions such as reaching or eye movements. Further, focusing on forms, colours, and object identity, signals must flow through the ventral stream into the inferior temporal cortex. For perceptual experience to arise, the visual cortex engages in recursive feedback loops with higher brain regions, for instance, temporal and parietal. Those feedbacks enter into loops between each other to continuously compare new sensory data with prior knowledge or expectations, leading to our visual recognition of the outer world.<ref name=":0" /> Along with Descartes analytical approach, raw light signals are simplified into features such as edges and movements by the visual cortex, then recombined under the guidance of attention and memory. This creates a synergy between modern neuroscience and analysing complex phenomena into smaller bits.<ref name=":6">Noller, F. (2021). ''Processing of information, building of truth''. Glossalab. <nowiki>https://www.glossalab.org/wiki/Processing_of_information,_building_of_truth</nowiki> </ref>  

Moreover, visual perception involves actively searching for relevant stimuli, influenced by external factors such as colour salience and movement, as well as internal states in order to recognise objects. For instance, conspicuous features can capture human attention instantly, leading to unusual preferences when distractions occur. In addition, the temporal cortex stores those representations, helping humans to categorise and label familiar objects in fractions of a second. Furthermore, visual search engages emotional and reward circuits when identifying form and motion. The ventral tegmental area and nucleus accumbens interact with cortical regions to process rewarding stimuli, reinforcing behaviour patterns triggered by appealing elements. Likewise, research shows that emotional associations are carried firmly throughout visual perception, which biases us towards or against objects before we consciously register the object. This phenomenon, known as microvalence, refers to subconscious evaluation of an object's aversiveness during visual processing.<ref name=":1">Jansson-Boyd, C. V., & Bright, P. (2023). Visual neuroscience. ''Elsevier EBooks'', 51–69. <nowiki>https://doi.org/10.1016/b978-0-443-13581-1.00004-2</nowiki> </ref>

Touch helps us to navigate through the physical space by integrating information from the skin, muscles, and joints to foster a cohesive perception of objects, surfaces, and spatial relationships. While joints and muscles enable feedback about an object's orientation and weight, the skin contains a complex system of specialised nerve endings designed to detect mechanical stimuli such as pressure, vibration, and texture.<ref name=":02">Reed, C. L., & Ziat, M. (2018). Haptic Perception: From the Skin to the Brain. ''Reference Module in Neuroscience and Biobehavioral Psychology''. <nowiki>https://doi.org/10.1016/b978-0-12-809324-5.03182-5</nowiki> </ref> The majority of receptors, which are distributed throughout the layers of the skin, are represented by:

At different rates of stimulation, each of the receptor types adapts continuously.<ref>Bayram-Weston, Zubeyde & Knight, John & Andrade, Maria. (2023). The senses 4: touch – physiology of the sensation and perception of touch. Nursing Times. 119. online. <nowiki>https://www.nursingtimes.net/neurology/the-senses-4-touch-physiology-of-the-sensation-and-perception-of-touch-13-12-2022/</nowiki></ref> Likewise, it converts physical energy (pressure, vibration, temperature) into electrical impulses, which are sent along nerve fibres towards the spinal cord, ensuring instantaneous awareness of haptic changes.<ref>Blumenrath, S. (2020). ''The Neuroscience of Touch and Pain''. Www.brainfacts.org. <nowiki>https://www.brainfacts.org/thinking-sensing-and-behaving/touch/2020/the-neuroscience-of-touch-and-pain-013020</nowiki> </ref> The electrical impulses are either transmitted through slowly adapting fibres, firing with persistent pressure, or rapidly adapting fibers. Once triggered, these signals travel to the somatosensory cortex, containing topographic maps of the skin, which represent different body parts.<ref name=":02" /> Furthermore, heating or cooling are detected by skin thermoreceptors influencing our recognition of objects (e.g., metal feels colder than plastic at room temperature). If an object begins to warm up or cool down in the hand, through feedback humans can then indicate material properties such as moisture. This overall process from touching to interpretation follows multiple pathways. First of all, the skin collects input with receptors (touch and vibration). Further, it leads to an awareness of the object's movement in order to judge its weight and orientation, which is defined as kinaesthetic feedback. This refers to the sense of limb movement, where muscles, tendons, and joints work together with inputs to inform the brain. Those information are then processed at the cortex and other parietal regions. Consequently, the multiple lines of sensory information offer a detailed and adaptive representation of the physical world.<ref name=":02" />

The interpretation of sound begins with sound waves defined as vibrations through a medium, for instance, air pressure, which travels through the outer ear channels towards the eardrum. The eardrums begin to vibrate and convey them through the middle ear bones into the fluid-filled cochlea of the inner ear. Further, the frequency being established in the basilar membrane of the cochlea disperses it to specific locations, forming a tonotopic map. Hair cells convert these mechanical vibrations into neural signals transmitted onwards the auditory nerve to the brain. However, due to finely arranged cochlear filters, a vast range of sound frequencies can be detected and separated into distinct pitches.<ref name=":2">Oxenham, A. J. (2018). How We Hear: the Perception and Neural Coding of Sound. ''Annual Review of Psychology'', ''69''(1), 27–50. <nowiki>https://doi.org/10.1146/annurev-psych-122216-011635</nowiki> </ref> Once the signals travel through the central auditory nerve, main sound properties such as amplitude and frequency are processed by the midbrain's inferior colliculus, while high frequency is received by the inferior colliculus, overlapping with pure auditory processing. However, before tactile high frequencies reach the inferior colliculus, they must pass through the pacinian corpuscles of the skin. Pacinian corpuscles are primarily touch receptors contributing to a better sound experience. This overall convergence suggests that touch and sound information being shared, thereby interchangeable neuronal circuits, being the reason therefore why we feel and hear music. This underlines the human capacity to distinguish numerous pitches due to the cochlea's ability to segregate frequencies precisely.<ref name=":2" /> In the same way, hearing a sound from different angles illustrates how inductive reasoning shapes the confidence we have in locating a pitch, leading to an overcross of auditory sensation and perceptual belief.<ref name=":6" />

Generally speaking, perceiving smell begins in the nose, where specialised olfactory receptors bind molecules. Correspondingly, humans possess approximately 396 functional receptor genes and many pseudogenes. These genes encode a large family of proteins found on the surface of cells. As a result of encoding these G protein-coupled receptors, cells can respond to thousands of potential molecules entering our nasal cavity. This binding creates an electrical signal that is transmitted to the olfactory bulb, where subtle scent differences are distinguished.<ref>Sharma, A., Kumar, R., Aier, I., Semwal, R., Tyagi, P., & Varadwaj, P. (2019). Sense of Smell: Structural, Functional, Mechanistic Advancements and Challenges in Human Olfactory Research. ''Current Neuropharmacology'', ''17''(9), 891–911. <nowiki>https://doi.org/10.2174/1570159x17666181206095626</nowiki> </ref>  

After initial processing in the olfactory bulb, that information is passed to the piriform cortex region, where odour identification occurs, while on the other hand the amygdala and hippocampus receive similar signals. The amygdala and hippocampus link smells to emotions and memories, contributing additionally to an experience of recollections.<ref>NeuroLaunch editorial team. (2024a). ''Brain and Smell: Exploring the Olfactory System’s Neural Pathways''. NeuroLaunch.com. <nowiki>https://neurolaunch.com/what-part-of-the-brain-controls-smell/</nowiki> </ref>  

Moreover, research suggests that the right orbitofrontal cortex (OFC) is essential for conscious olfactory awareness. As depicted in a case, individuals with damage to the right OFC can partially respond to smell while being unaware of it. Even though odour processing occurs at the piriform cortex or left OFC, a full smell perception requires the connectivity of all involved brain regions.<ref>Li, W., Lopez, L., Osher, J., Howard, J. D., Parrish, T. B., & Gottfried, J. A. (2010). Right Orbitofrontal Cortex Mediates Conscious Olfactory Perception. ''Psychological Science'', ''21''(10), 1454–1463. <nowiki>https://doi.org/10.1177/0956797610382121</nowiki> </ref> Nevertheless, the interplay between smell, memory, and emotion is profound, hence it can evoke memories and shape our affective mood.

The idea of taste starts with taste visual buds found across the tongue's surface—called papillae, where each bud contains receptor cells, supporting cells, and basal cells.<ref>Henley, C. (2021). ''Taste''. Openbooks.lib.msu.edu; Michigan State University Libraries. <nowiki>https://openbooks.lib.msu.edu/neuroscience/chapter/taste/</nowiki> </ref> Flavours such as sugars or bitter alkaloids are detected by those cells and converted into electrical signals. The signals are then transmitted via the cranial nerves to the brainstem and thalamus before reaching the primary gustatory cortex, where flavour information is perceived and processed.<ref>NeuroLaunch editorial team. (2024b). ''Brain’s Taste Control Center: Mapping the Neural Pathways of Flavor Perception''. NeuroLaunch.com. <nowiki>https://neurolaunch.com/what-part-of-the-brain-controls-taste/</nowiki> </ref>  

Besides the gustatory cortex, taste, smell, and texture are also processed by the orbitofrontal cortex, influencing decisions about consumption behaviour. In comparison, certain tastes evoke memories being attributable to the amygdala, while the hypothalamus contributes by regulating appetite and taste preferences. However, flavour depends, as research depicts, further from genetics, ageing, and neurological conditions. This underlies that the function of taste involves numerous neural circuits ensuring that each bite resonates beyond the tongue.<ref>Trivedi, B. P. (2012). Neuroscience: Hardwired for taste. ''Nature'', ''486''(7403), S7–S9. <nowiki>https://doi.org/10.1038/486s7a</nowiki> </ref>

Dualism proposes that perceiving is not a one-dimensional outcome of physical processes in the brain, rather, it involves a separate mental dimension that shapes our conscious experience. Accordingly, the idea of Descartes argues that the mind is indeed a thinking substance distinct from the body's extended substance. This aligns with Plato's views, where the soul is held to be immaterial and intellectually with higher being forms.<ref name=":5" /> While eyes, ears, and other organs receive physical data, our conscious perception exceeds these signals, and we are therefore accountable for our intentional and subjective interpretation within our mental realm. For this reason, the dualism claims that physical explanations cannot resolve the pure nature of sensory experience. For instance, when viewing a striking painting, the sensation is tangled to the subjective awareness in a way where no objective, third-person description of the painting's properties could evoke the same experience. Therefore, if mental events were only based on physical circumstances, then anyone using the right instruments could equally observe, yet first-person experiences resist such observations. Nonetheless, whether the mental district is a separated substance or not, dualism demands that understanding true perception requires more than physical causation alone.<ref name=":5">Robinson, H. (2020). ''Dualism''. Stanford Encyclopedia of Philosophy. <nowiki>https://plato.stanford.edu/entries/dualism/</nowiki> </ref>

Perception requires a causal link between an external object and the perceiver's sensory experience following the causal theory. We see, hear, or smell an object if that object itself brings the relevant sensory experiences. This principle can be illustrated by the thought experiment where a blocked pathway (e.g., a mirror) exists in front of the person and the pillar behind the person, no direct causal relationship exists, and therefore the pillar cannot be truly perceived. In this scenario, the mirror redirects the light from the actual pillar to the eyes, and therefore the individual cannot perceive the intended object. Likewise suggested by Hyman, a person lacks true perception if the external object is not causing the experience. This applies across modalities of vision, auditory, and olfaction for intuitive judgement in "Blocker cases" (e.g., a mirror redirecting) and "Non-Blocker cases" (e.g., brain stimulation producing similar experience). However, some individuals diverge from those intuitive philosophical standpoints, where participants believe that genuine perception can occur even in non-Blocker scenarios, as shown by studies.<ref>Roberts, P., Allen, K., & Schmidtke, K. (2020). Reflective Intuitions about the Causal Theory of Perception across Sensory Modalities. ''Review of Philosophy and Psychology'', ''12''(2), 257–277. <nowiki>https://doi.org/10.1007/s13164-020-00478-6</nowiki> </ref> This discrepancy raises questions about whether causal condition is truly a conceptual truth for perception. Thereupon, this mismatch illustrates that individuals assume perception might be conceivable only on brain stimulation, implying an exposure without physical obstruction.   

Direct realism suggests that the perception of objects such as chairs, books, or cups of coffee arises from our engagement with them, rather than mere mental images. A sensible idea for this implies that objects exist independently of any perceiver's awareness. Hence, direct realism can be divided into naïve realism and scientific realism. According to naïve realism, objects retain all perceived properties, for example, colour or surface texture, regardless of the observation. In contrast, scientific realism argues that certain examined qualities (e.g., sweetness) depend on the examiner, while mass or shape persist irrespective of observation. Likewise, Locke's notion of primary (e.g., size, motion) versus secondary (e.g., colour, taste) qualities aligns partially, whereas primary exists objectively and secondary dispositional. However, both assert fundamentally that the senses must be in direct contact with the external reality.<ref name=":4">O’Brien, D. (n.d.). ''Perception, Objects of | Internet Encyclopedia of Philosophy''. Internet Encyclopedia of Philosophy. <nowiki>https://iep.utm.edu/perc-obj/</nowiki> </ref>

Perception is a representational relationship linking conscious experience to the external world in virtue of their content rather than any direct sensory object following the intentional theory.<ref name=":4" /> However, we perceive a chair not by apprehending a mental entity, but by adopting a perceptual state that possess intentional content. This suggests that our perceptual state inherently carries representations (e.g., there is a chair) that manifest the existence of objects within our mind. Therefore, seeing a bent stick in water is experienced still as a bent stick despite the fact that the stick might be straight in the physical reality. Likewise, those illusions demonstrate cases where the world is misaligned with the mind's interpretation, yet the representational object remains intact within the human.<ref>Mcintyre, R., & Smith, D. W. (1989). ''Husserl’s Phenomenology: A Textbook'' (pp. 147–179). Original. <nowiki>https://www.csun.edu/~vcoao087/pubs/intent.pdf</nowiki> </ref> Moreover, when referring to intentionality, perception is defined as resembling beliefs or other attitudes, which postulates that illusions involve representational states that fail to match external objects or their properties. This concludes that intentionalism does not require the postulation of mental intermediaries, for instance, sense data.<ref name=":4" />

A sensible idea for this theory is its core distinction between the veridical (mind-independent object) and non-veridical (illusion or hallucination) perception. The veridical states that the human observes a mind-independent object in the world (e.g., a real cup in front of you) involving the actual external object, whereas non-veridical defines illusory or hallucinatory experiences as not genuinely seeing a mind-independent object. For this reason, J.M. Hinton argued that veridical perception and hallucination do not need to share a common nature, implying that even when both are indistinguishable from the inside, they do not share identical intrinsic properties.<ref>Soteriou, M. (2009). ''The Disjunctive Theory of Perception (Stanford Encyclopedia of Philosophy)''. Stanford.edu. <nowiki>https://plato.stanford.edu/entries/perception-disjunctive/</nowiki> </ref> In contrast, intentionalism proposes that both those experiences share an internal representation of which one happens to match reality, while disjunctive theory denies a shared mental representation for both experiences. Hence, seeing a cup in front of oneself, the cup belongs partly to the perceptual state, because its properties create in part the nature of one's perception. Whereas in hallucination, there does not exist such a real cup forming a part of the experience. This difference is displayed by disjunctivism, either seeing actually a cup, where the external object is present, or merely undergoing a hallucination, being entirely internal and absent from the real object.<ref name=":4" /> Thereupon, disjunctivism embraces a form of externalism, stating that identical brain states alone cannot guarantee the same perceptual state, due to the veridical experience that involves an actual object in the presence to be experienced.  If the neural processes remain the same while observing the object, but the external object disappears (e.g., a person shifts to a hallucination), the mental state changes from the ground on, once the subject is no longer the same type of the perceptual state. Thus, both veridical and non-veridical do not share an internal representation.<ref name=":4" />

The Beholder's Share, first introduced by Alois Riegl, later elaborated by Ernst Gombrich, highlights how each viewer actively completes an artwork. Sensory elements such as colours, patterns, shapes, or scenic details initially shape our perception of the piece. However, top-down processes, like prior expectations or learnt associations, further refine our conscious vision. Certainty, perception involves the interpretation and integration of sensory stimuli and expectations, unlike sensing relying only on raw detection of stimuli.<ref name=":3">Seth, A. K. (2019). From Unconscious Inference to the Beholder’s Share: Predictive Perception and Human Experience. ''European Review'', ''27''(3), 378–410. <nowiki>https://doi.org/10.1017/s1062798719000061</nowiki> </ref> For this reason, can perception be seen as an active construction of experience, while sensing as a passive reception of information. Due to the heavily influential nature of context, information about the artist's life or familiarity with their work of art can dramatically shift interpretation, illustrating that the viewer's knowledge and beliefs co-create an artwork's effect. Moreover, the artist's intentions often differ from those of the observer. This lack or conflict of context can completely redirect the emotional or intellectual experience of an artwork. Following this interplay between stimulus input and the observer's framework undermines the deeper principle that perception emphasises a projection of one's internal model onto the external features to construct meaning.<ref name=":3" /> As a result, the physical properties of the artwork itself emerge as much from the viewer's interpretive engagement.