Quality spaces

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Quality spaces are intended to model mental qualities, understood as "the mental properties in virtue of which an individual can perform perceptual discriminations".[1]

Quality spaces need to be distinguished from qualia spaces, though the precise relation is not yet clarified. A proposal would be to conceive of qualia spaces as taking the specific characterizations or properties of qualia into account, whereas quality spaces only refer to mental qualities as defined above.

Mental Qualities

Mental qualities are defined to be "the mental properties in virtue of which an individual can perform perceptual discriminations"[1]. Several authors take the term 'mental quality' to be generally synonymous to qualia or phenomenal consciousness, however it is agreed that the term mental qualities so defined could also refer to unconscious properties.

Mental qualities are distinguished from perceptible qualities and physical stimuli presented to a subject.

Proposed Mathematical Structures

The elements of quality space represent mental qualities. At least two different formal models have been proposed:

Standard Framework

In the standard framework, mental qualities are elements of a metric space, where the distance represents phenomenal similarity.[1]

Regional Framework

The regional framework has been developed in order to overcome problems of the standard framework.[2] In the metric space of the standard framework, it identifies subsets of the metric space, called regions, which are taken to represent mental qualities instead of the points of the metric space, thereby attempting to represent phenomenal property of precision. A pseudo-metric is defined on the regions in dependence on the metric of the underlying metric space.

Epistemological Considerations

The metric space of the standard framework is constructed operationally by use of Just Noticeable Differences or Matching. Since it is also compatible with non-conscious perceptual discriminations, it stands to reason that this space is largely conceived of as epistemic or operational in nature. In contrast, the regional framework is more phenomenological in nature, representing conscious experience mathematically.


  1. 1.0 1.1 1.2 Rosenthal, David. "Quality spaces and sensory modalities." The Nature of Phenomenal Qualities: Sense, Perception, and Consciousness (2015): 33-65.
  2. Lee, Andrew. "Modeling Mental Qualities". Philosophical Review