When is a weight not illusory?

Weight illusions occur whenever some aspect of an object--such as its size, material or colour--arouses the expectation that its weight will be heavier or lighter than it actually is. The direction of the illusion normally contrasts with the expected weight. When objects are hidden from sight and lifted by strings they can provide no misleading cues, and a correct weight-expectation should be achieved after one or two trials. When a visible object has the same physical and apparent weight as a hidden object, it can be defined as non-illusory. Weighted tins and polystyrene blocks of various sizes were compared with hidden weights. Tins were found to be non-illusory when their density was about 1.7, and polystyrene blocks when their density was about 0.14.

Weight illusions may be due to a central scaling process which enables a wide range of weights to be estimated, different ranges being selected according to the expected value of the weight. If the selected range is inappropriate an illusion occurs. Changes in expected value could also allow for the operation of “weight-constancy” during changes in proprioceptive stimulation.     

Is the weber fraction a function of physical or perceived input?

It is well known that a given physical input (e.g. intensity of light or sound, length or weight of an object) does not always give rise to the same sensation. For example, arrow heads affect the perceived length of lines (Muller-Lyer illusion) and size affects the apparent weight of an object (size-weight illusion). It is generally assumed that the differential threshold is a simple function of the physical intensity of the stimulus. We may however ask whether the differential threshold is affected by illusions.

To try to answer this question we estimate differential thresholds under a pair of conditions in which the relevant input is the same but appears different. Using the size-weight illusion, we have found that the differential threshold for weight is greater for a set of small weights than for a set of larger and apparently lighter weights.     

Conditional permission in deontic logic

Conclusion In the face of the considerations set forth above, I submit that Anderson's proposed definition (D) does not represent an acceptable construction of the concept of conditional permission. This, in turn, suggests that conditional permission must be viewed as a viable deontic relationship in its own right, and is not definable in terms of unconditional deontic concepts. It appears, then, that a reduction of conditional to unconditional deontic logic is not warranted.     

A remark on tucker and Messick's “points of view” analysis

It is shown that to combine readings from points of view configurations as assumed in Tucker and Messick's model is not to combine configurations in any simple way. Both empirical and logical consequences of the disparity are discussed.