Varieties of perception 45
perceiving organism is able to match his position, movements and aims against
the relevant environmental invariants over time, thereby using proprioceptual
information. Both sets of relations in conjunction are the informational relations
that specify, in Gibson’s phrasing, the environment for the organism. Third, the
organism must be in a condition suitable to actually picking up that information. Precisely if and when both the environment- and the organism-bound conditions are fulfilled, there will be a direct perception of affordances: the perceiving
organism is enabled to immediately rely on the relation between himself and what
remains invariant, what varies regularly and what varies arbitrarily in an object
over the course of his perceptual activities.
For thus including organism-related variables, information in the ecological
sense is “intrinsic” to a perceptual situation, as distinguished from “extrinsic”
information that allows for absolute, perceiver-independent measurements of
physical and physiological variables by an external observer. Intrinsic, affordancerelated information still allows for measurement, although on a different basis
(see Gibson 1979, 128). The paradigm of measurement-oriented approaches in
post-Gibsonian ecological psychology are the measurements of stair-climbing
affordances for persons of different leg lengths in William J. Warren’s study
(1984, where the intrinsic/extrinsic distinction is introduced; see also Boumans
2013). Although there is considerable variance in the relation between riser
heights and leg length for short and tall persons, the results of the experiments in
this study suggest that there are ratios for stair-climbing affordances that remain
constant across the study population. These ratios can be expressed in an intrinsic
or body-scaled metric that matches the dimensions of the subjects’ bodies and the
dimensions of the object in question – in this case, the riser height of the stairs.
Such ratios can be found both for perceptual category boundaries – between stairs
that are perceived as still being climbable and stairs that are already perceived as
being unclimbable – and for optimal heights in terms of effort to be invested into
climbing. The ratios are such that short people will perceive the same affordance
for relatively low risers that will be perceived by tall people for proportionally
higher risers. The ratios, however, do not express subjective factors, in that they
remain constant across the population, with identical absolute measures for people of the same size, and in that perceived optimal heights quite closely match the
actual energetic optima in physiologically based trials. Hence, Warren concludes,
environmental objects are perceived by an organism in relation to his action capabilities, where that relation is rather stable and unequivocal.
On this background, affordances can be relationally defined, in a two-step fashion that builds upon informational relations and the perceiving organisms’ abilities to track, and act upon, these relations – which will include his own specific
relations to his environment. This relational view allows for a fairly clear set of
distinctions to be made with respect to situations in which an affordance, as it is
perceived by an organism, and information for perception do not appear to match:
there is no information if the relations between signalling and signalled world
affairs are not unequivocal, even if and when an organism appears to track such a
relation, so there is no affordance to be perceived either. Conversely, if there is a
perceiving organism is able to match his position, movements and aims against
the relevant environmental invariants over time, thereby using proprioceptual
information. Both sets of relations in conjunction are the informational relations
that specify, in Gibson’s phrasing, the environment for the organism. Third, the
organism must be in a condition suitable to actually picking up that information. Precisely if and when both the environment- and the organism-bound conditions are fulfilled, there will be a direct perception of affordances: the perceiving
organism is enabled to immediately rely on the relation between himself and what
remains invariant, what varies regularly and what varies arbitrarily in an object
over the course of his perceptual activities.
For thus including organism-related variables, information in the ecological
sense is “intrinsic” to a perceptual situation, as distinguished from “extrinsic”
information that allows for absolute, perceiver-independent measurements of
physical and physiological variables by an external observer. Intrinsic, affordancerelated information still allows for measurement, although on a different basis
(see Gibson 1979, 128). The paradigm of measurement-oriented approaches in
post-Gibsonian ecological psychology are the measurements of stair-climbing
affordances for persons of different leg lengths in William J. Warren’s study
(1984, where the intrinsic/extrinsic distinction is introduced; see also Boumans
2013). Although there is considerable variance in the relation between riser
heights and leg length for short and tall persons, the results of the experiments in
this study suggest that there are ratios for stair-climbing affordances that remain
constant across the study population. These ratios can be expressed in an intrinsic
or body-scaled metric that matches the dimensions of the subjects’ bodies and the
dimensions of the object in question – in this case, the riser height of the stairs.
Such ratios can be found both for perceptual category boundaries – between stairs
that are perceived as still being climbable and stairs that are already perceived as
being unclimbable – and for optimal heights in terms of effort to be invested into
climbing. The ratios are such that short people will perceive the same affordance
for relatively low risers that will be perceived by tall people for proportionally
higher risers. The ratios, however, do not express subjective factors, in that they
remain constant across the population, with identical absolute measures for people of the same size, and in that perceived optimal heights quite closely match the
actual energetic optima in physiologically based trials. Hence, Warren concludes,
environmental objects are perceived by an organism in relation to his action capabilities, where that relation is rather stable and unequivocal.
On this background, affordances can be relationally defined, in a two-step fashion that builds upon informational relations and the perceiving organisms’ abilities to track, and act upon, these relations – which will include his own specific
relations to his environment. This relational view allows for a fairly clear set of
distinctions to be made with respect to situations in which an affordance, as it is
perceived by an organism, and information for perception do not appear to match:
there is no information if the relations between signalling and signalled world
affairs are not unequivocal, even if and when an organism appears to track such a
relation, so there is no affordance to be perceived either. Conversely, if there is a