Perception / gnosis

What is perception and gnosis?

Perception and gnosis is a fundamental cognitive area, which helps us recognize functions of objects and plan everyday activities. This cognitive area includes the ability to process incoming visual stimuli, to understand spatial relationships between objects, and to visualize images and scenarios (Michelon 2006).

Perception and gnosis is the ability of the brain to recognize previously learned information such as objects, persons, or places collected from our senses. Thus, there are different types of perception and gnosis, one for each sensory modality:

  • Visual perception and gnosis: the ability to recognize different stimuli (objects, faces, colors, shapes) by sight and assign meaning to them.
  • Auditory perception and gnosis: the ability to recognize different stimuli (sounds) by hearing.
  • Tactile perception and gnosis: the ability to recognize or identify different stimuli (texture, objects, or temperature) by touch.
  • Olfactory perception and gnosis: the ability to recognize different stimuli (odors) by smell.
  • Gustatory perception and gnosis: the ability to recognize different stimuli (flavors) by taste (Neuronup, 2012-2017).

Psychologists typically make a distinction between sensation and perception. Sensations are uninterpreted sensory impressions created by the detection of environmental stimuli, whereas perception refers to the set of processes by which we make sense of these sensations (Introduction to perception, 2009).

Sensations are created when we detect stimuli by our senses (smell, sight, touch, hearing, taste) from the environment (Introduction to perception, 2009). Sensory inputs from eyes, ears, nose etc. are converted into perceptions of objects (sights, sounds, smells, taste and touch experiences) (McLeod, 2008). Perception is therefore the organization, identification, and interpretation of sensory information  that helps us represent and understand the environment. Perception is not the passive receipt of sensory inputs; it is shaped by learningmemoryexpectation, and attention.

Approaches to information processing can be top-down or bottom-up. Top down approaches include knowledge or expectations of an individual, which guide processing. In bottom-up approaches there is data being put together until a bigger picture is formed (Introduction to perception, 2009).

Visual processing is composed of different stages (Marr, 1982): early, intermediate, and late vision. Roughly, at early stages of the visual system, processes like segregation of figure from background, border detection, and the detection of basic features (e.g., color, orientation, motion components) occur. This information reaches intermediate stages, where it is combined into a temporary representation of an object. At later stages, the temporary object representation is matched with previous object shapes stored in long-term visual memory to achieve visual object identification and recognition. While early visual processes are largely automatic and independent of cognitive factors, late visual stages are more influenced by our knowledge (Raftopoulos, this issue). Examples of cognitive influence on how we perceive the world – that modulates late vision – are visual search and attention (Treisman, 1993).

The process of perception and recognition can be divided into different stages. Firstly, there is processing of basic object components, such as colour, depth, form or texture (Humphreys, Price and Riddoch, 1999; Kolb and Whishaw, 2003). Then, these components are categorized or grouped on the basis of similarity (Humphreys, Price in Riddoch, 1999), which requires directing and switching attention between various aspects of the objects (Kolb in Whishaw, 2003). The representation of the input is then matched with descriptions in our memory (Humphreys, Price in Riddoch, 1999). In the end, semantic attributes are applied to the representation, providing meaning and recognition (Humphreys, Price in Riddoch, 1999).

Therefore, object recognition is the ability to perceive physical properties of an object (shape, color, texture) and apply semantic attributes to it (identifying the object as a table). It is also necessary to understand the use of the object, its relationship to other objects and previous experience with the object (Enns, 2004). The forms of recognition include identification, categorisation and discrimination. The basis for all these abilities is the encoding of spatial information derived through perceptual experience (Christou in Bülthoff, 2000 in Wallis and Bülthoff, 1999). The hippocampus has an important role in object-recognition and memory functions, so it is very important in organizing memories of objects in space (Kolb in Whishaw, 2003).


Why is perception and gnosis important at the functional level?

Perception and recognition help us make sense of the world around us and orient in the environment. It enables us to navigate through the world, make decisions, prepare for action and avoid danger (Introduction to perception, 2009). For example, knowing the colour or shape of an object helps a person to identify quickly a particular object in a complex visual scene (Wolfe and Horowitz, 2004). It is easier for us to be independent or to feel self-confident in finishing specific activities. With the help of perception and gnosis, individuals maintain their favourite tasks or structure and their daily routine adjusted to their needs, interests and wishes.  Perception and gnosis are of vital importance in our daily life performance. They bring us satisfaction and enable us to develop our potentials. We also become more active in a society. If we illustrate: Life would be difficult if one could not recognize their close relatives, identify their favourite song, identify certain parts of your body as their own or not recognize what cutlery is used for (Neuronup, 2012-2017).

Finally, it is also important in communication and social relationships as it enables us to make sense of the people around us. We are experts at detecting and identifying faces, which is mostly due to our ability to perceive faces as a whole and not only as individual parts not connected to one another.


Alterations in this dimension in patients with AD

Perception and gnosis are controlled by right hemisphere of brain. Cognitive impairment, as recognized by individuals with dementia leads to lower efficacy of visual perception and gnosis. Persons with AD have problems with depth perception, distorted and blurred vision and reduced ability to distinguish colour shades. In most cases, people with dementia also find it disturbing, when dealing with contrasting colours.

Persons with Alzheimer’s disease can have difficulties recognizing objects due to impairment of semantic memory, which is used to retrieve information regarding naming and categorizing objects (Laatu, Jaykka, Portin and Rinne, 2003).

Agnosis is the inability to process sensory information. Often there is a loss of ability to recognize objects, persons, sounds, shapes, or smells while the specific sense is not defective. Most common in Alzheimer’s disease are visual agnosis and prosopagnosis.

Visual agnosis is an inability to combine individual visual impressions into complete patterns, that leads to inability to recognize objects and in consequence an inability to draw or copy them (Kolb and Whishaw, 2003).

Prosopagnosis (inability to recognize faces) occurs mostly in the early stages of the disease. It seems that there is not only the problem with recognizing faces, but that the processes at the stage of visual face perception are impaired. Individual facial features, such as the eyes, nose or mouth, are not perceived as a whole and therefore not recognized as a face. This also gravely impairs person’s communication and orientation in social contexts.

As perception and recognition play a fundamental role in our orientation and navigation, it is common for persons with Alzheimer’s disease to wander and get lost frequently. Being ‘lost’ is usually the result of being in an unfamiliar environment, which blocks them to approach defined destination (Christou in Bülthoff, 2000). Visuospatial function is even more impaired in the cases of DLB as in the ones with Alzheimer’s disease (Calderon et al., 2001).


Serious games, appropriate for this dimension

AD-GAMING games:

Similar games:

  • Domino
  • 3D logic puzzles
  • Easy tip
  • Katamino
  • Classification cards
  • Association cards


  • Christou, C. in Bülthoff, H.H. (2000). Perception, representation and recognition: A holistic view of recognition. Spatial vision, 13 (2,3), str. 265-275.
  • Enns, J. T. (2004). The Thinking Eye, The Seeing Brain: Explorations in Visual Cognition. New York:
  • Norton & Company.
  • Gnosis (2012-2017). Acquired from
  • Humphreys, G., Price, C., & Riddoch, J. (1999). From objects to names: A cognitive neuroscience approach. Psychological Research , 62, 118-130.
  • Kolb, B. in Whishaw, I.Q. (2003). Fundamentals of human neuropsychology. New York: Worth Publishers.
  • Laatu S., Jaykka H., Portin R., Rinne J. (2003). Visual object recognition in early Alzheimer’s disease: deficits in semantic processing. Acta Neurologica Scandinavica, 108, 82–89.
  • McLeod,                         (2008).           Visual                       Perception      Theory.               Acquired                 from
  • Michelon, P. (2006). What are Cognitive Abilities and Skills, and How to Boost them? Acquired from
  • Introduction to                      perception                     (2009).                      Acquired                      from
  • Why people with Alzheimer’s stop recognizing the faces of loved ones? (2016) Acquired from