The location and interpretation of the bisection point

In atemporal bisectiontask with humans, the observer is required to decide whether a probe duration ( t ) is more similar to the short referent (S), an R S response, or to the long referent (L), an R L response. Temporal bisection yields a psychometric function relating the proportion of long responses, P(R L ), to probe duration t . The value of t at which R S and R L occur with equal frequency, P(RL) = .5, is referred to as the bisection point, T 1/2 . Bisection models usually interpret T 1/2 as identifying the value of t that is equally confusable with S and L, but they differ in their predictions for the location of T 1/2 . The present paper presents new data relevant to the location and interpretation of T 1/2 . The data indicate that the empirical values usually are biased, the biases being influenced by duration range, L:S ratio, and probe spacing. Moreover, the biases often are not consistent across observers. It is concluded that empirical values of T 1/2 should not be interpreted as indicating the value of t that is equally confusable with S and L.     

The bisection point across variants of the task

Bisection tasks are used in research on normal space and time perception and to assess the perceptual distortions accompanying neurological disorders. Several variants of the bisection task are used, which often yield inconsistent results, prompting the question of which variant is most dependable and which results are to be trusted. We addressed this question using theoretical and experimental approaches. Theoretical performance in bisection tasks is derived from a general model of psychophysical performance that includes sensory components and decisional processes. The model predicts how performance should differ across variants of the task, even when the sensory component is fixed. To test these predictions, data were collected in a within-subjects study with several variants of a spatial bisection task, including a two-response variant in which observers indicated whether a line was transected to the right or left of the midpoint, a three-response variant (which included the additional option to respond “midpoint”), and a paired-comparison variant of the three-response format. The data supported the model predictions, revealing that estimated bisection points were least dependable with the two-response variant, because this format confounds perceptual and decisional influences. Only the three-response paired-comparison format can separate out these influences. Implications for research in basic and clinical fields are discussed.     

The Lindenbaum fixed point algebra is undecidable

We prove that the first order theory of the fixed point algebra corresponding to an r.e. consistent theory containing arithmetic is hereditarily undecidable.     

The reliability of a point biserial coefficient of correlation

An attempt is made to elaborate upon Lev's results concerning the reliability of the point biserial coefficient of correlation in a manner that will be helpful to the psychological statistician. Procedures required in the use of the non-centralt tables prepared by Johnson and Welch are described as they relate to the determination of the fiducial limits for a point biserial coefficient. A normal approximation technique for the estimation of fiducial limits is also suggested. Numerical evidence is presented which shows that relative to a given level of significance the width of the fiducial interval estimated from a point biserial coefficient of any size is smaller than that of the fiducial interval corresponding to an ordinary Pearsonian coefficient of the same magnitude.     

The effect of the uniqueness point in spoken-word recognition

Summary The study examines the possibility of observing on-line recognition of spoken words through manipulations of the location of the uniqueness point (UP) in a gender-classification task. The subjects were presented with spoken French nouns and had to indicate by a key-press response whether each was feminine or masculine. RTs measured from word onset were significantly correlated with UP location, a finding that supports the notion of on-line processing. The effect of UP location is, however, smaller than that predicted by the original cohort theory (that recognition occurs exactly at the UP). On the other hand, it is stronger when words with respectively early and late UPs are presented in homogeneous blocks rather than in mixed order. It is proposed that the results can be accounted for by the notion of a sub-optimal lexical strategy in which some monitoring of the phonetic data continues past the UP.     

The effect of fixation point on the appearance of rectilinearity

Data from two experiments indicate that (a) within 3.5 deg visual angle of the fixation point, an eccentrically fixated line and dot appear rectilinear when they are objectively convex toward the fixation point; (b) beyond 3.5 deg, they appear rectilinear when they are objectively concave; (c) the latter effect is not an artifact of the use of stationary fixation points; and (d) the addition of an extraneous line to the stimulus line so as to form a 90-deg angle acts as if to reduce the apparent size of the angle, but does not alter fixation point effects. The data were interpreted as supporting (a) the hypothesis that the stimulus line was more sensitive to illusory distortion than the dot, and (b) the ID (increasing-decreasing) model of the visual field—an inner area of increasing concentric contraction (stimuli appear to lie nearer the fixation point to a degree which increases with distance from the fixation point) is bounded by an outer area of decreasing concentric contraction.     

The idea of emancipation from a cosmopolitan point of view

R. Rorty uncouples cosmopolitanism from emancipation and rejects the latter on both phylogenetic and ontogenetic grounds. Thus: 1. There is no human nature to be emancipated, and 2. The notion of a rational, transcendental and conditioning subject (presupposed by traditional theories of emancipation) is obsolete. He preserves the idea of cosmopolitanism, which, in an effort to avoid foundationalisrn, he associates only with the development and progress of liberal societies. His cosmopolitanism relies on the distinction between persuasion and force and his preference for conversation over rational discourse. In this paper, I discuss Rorty's claims and trace residues of biologism, positivism, and behaviourism in them. By putting forward an immanent critique of Rorty's account of cosmopolitanism and emancipation, I defend a non-foundationalist notion of redemption as self-realization and propose a new justification of Rorty's distinction between force and persuasion.     

The conflict over creation from a medieval point of view

Many theological terms such as ‘causation’ and ‘creation’ carried technical meanings during the late thirteenth century but these same terms are often treated commonly in modern discourse. When the tension between creationism and evolution is examined in light of what well known medieval theologians wrote, it appears that the current debates related to evolution often lapse into the fallacy of equivocation. One unfortunate consequence of this breakdown is that the root of the problem, the subtle language involved, often remains unexposed. Moreover, the level of passionate discourse surrounding evolution suggests that a nearly scholastic approach is required if further confusion is to be limited.