Osvaldo Da Pos

Balanced and unbalanced, complete and partial transparency

Beck, Prazdny, and Ivry’s (1984) interpretation of Metelli’s theory of phenomenal transparency is reexamined here. There are no constraints, because the theory considers only balanced transparency and nothing is asserted against the existence of forms of unbalanced transparency. Experiment 4 of the present study proves that conditions of intensity are primary for complete balanced transparency and cannot be overcome if figural conditions strongly suggest transparency. The equation α = (p−q)/(a−b) does not require further restrictions because the cases cited by Beck et al. concern nonbalanced transparency. Experiment i proves that figural conditions cannot be considered primary and thus be the cause of the perception of transparency. The present paper reports that, contrary to the results Beck et al. obtained in their Experiment 4, a series of experiments in which experienced subjects were used and in which estimation of transparency was compared with predictions calculated with the α formula gave satisfactory results. Beck et al.’s thesis, according to which α ∈ α′ hinders transparency whereas t ∈ t′ allows it, is confirmed. Experienced subjects and simple instructions appear to yield clearer results.

Chromatic induction in neon colour spreading

Neon colour spreading occurs when sections of a lattice are replaced by segments of a different colour. This colour appears to diffuse out of the segments, and produce a slightly tinted transparent surface floating above the lattice. In two of the four experiments reported here, observers varied the colour of an area in a test display, until it matched the neon colour perceived in a corresponding (illusory) area in a comparison display. We found that the neon colour is an additive mixture of the colour of the segments and the colour complementary to the lattice, as suggested by Bressan (Vision Research 35 (1995) 375). In the other two experiments, we separately manipulated the presence and alignment of lattice and segments, to test whether the neon effect is fully predicted by a combination of colour diffusion and simultaneous colour contrast. We found that the colour induced in a neon figure is more saturated than the colour induced in a comparable non-neon figure. We discuss the implications of these results on our current understanding of the mechanisms of neon colour spreading.

The Müller-Lyer illusion in the teleost fish Xenotoca eiseni

In the Müller-Lyer illusion, human subjects usually see a line with two inducers at its ends facing outwards as longer than an identical line with inducers at its ends facing inwards. We investigate the tendency for fish to perceive, in suitable conditions, line length according to the Müller-Lyer illusion. Redtail splitfins (Xenotoca eiseni, family Goodeidae) were trained to discriminate between two lines of different length. After reaching the learning criterion, the fish performed test trials, in which they faced two lines (black or red) of identical length, differing only in the context in terms of arrangement of the inducers, which were positioned at the ends of the line, either inward, outward, or perpendicular. Fish chose the stimulus that appear to humans as either longer or shorter, in accordance with the prediction of the Müller-Lyer illusion, consistently with the condition of the training. These results show that redtail splitfins tend to be subject to this particular illusion. The results of the study are discussed with reference to similar studies concerning the same illusion as recently observed in fish. Contrasting results are presented. The significance of the results in light of their possible evolutionary implications is also discussed.

Test of the Singh-Anderson Model of Transparency

A new model of achromatic transparency has been recently proposed by Singh and Anderson as an alternative to the model proposed long ago by Metelli. The study reported here compared these models using achromatic stimuli consisting of a transparent disk on a background formed by two adjoining rectangles, with the common border of the rectangles dividing the disk in half. Let a and b denote the luminances of the left and right parts of the background, respectively, and let p and q denote the luminances of the left and right parts of the disk, respectively. The value of b was varied for fixed values of a, p, and q. For these values the Singh-Anderson model predicts that the perceived extent of transparency T of the disk is constant with b, while Metellis model predicts that T decreases as b increases. Participants rated T. The results confirm the prediction of Metellis model. It is also shown that the Singh-Anderson model is invalid in principle in that, unlike Metellis model, it fails to capture the principle of independence of the effects of a, b, p, and q on T.

Is Vivaldi smooth and takete? Non-verbal sensory scales for describing music qualities

Studies on the perception of music qualities (such as induced or perceived emotions, performance styles, or timbre nuances) make a large use of verbal descriptors. Although many authors noted that particular music qualities can hardly be described by means of verbal labels, few studies have tried alternatives. This paper aims at exploring the use of non-verbal sensory scales, in order to represent different perceived qualities in Western classical music. Musically trained and untrained listeners were required to listen to six musical excerpts in major key and to evaluate them from a sensorial and semantic point of view (Experiment 1). The same design (Experiment 2) was conducted using musically trained and untrained listeners who were required to listen to six musical excerpts in minor key. The overall findings indicate that subjects’ ratings on non-verbal sensory scales are consistent throughout and the results support the hypothesis that sensory scales can convey some specific sensations that cannot be described verbally, offering interesting insights to deepen our knowledge on the relationship between music and other sensorial experiences. Such research can foster interesting applications in the field of music information retrieval and timbre spaces explorations together with experiments applied to different musical cultures and contexts.

Illusory illusions: the significance of fixation on the perception of geometrical illusions.

Some well-known geometrical illusions disappear when the eyes are fixating and saccades are suppressed for a period of time. This disappearance is not accompanied by fading due to stabilisation of the retinal image. Any saccade made on purpose restores the illusion immediately. The fixation time after which some illusions disappeared was measured for four illusions and four subjects each. Effects of practice have been observed after measurements were repeated on successive days. Present theories of vision cannot readily explain the effect.

How >:( is Bizet? Icon ratings of music

Can music be rated consistently using icon descriptors without verbal mediation? Sixty-eight participants rated six experimenter- and two self-selected pieces of music along 15 bipolar icon scales intended to portray emotions, and sensory experiences involving color, temperature, shape, speed, texture, and weight. Several replications were reported, including Mozart being blue, Brahms being soft and Bizet being takete (a jagged shape). Crossmodal associations with individual pieces were similar to those reported in previous studies, but self-selected liked and disliked musics did not evoke as many such associations, leading to the conclusion that crossmodal perception may be indicative of music character more so than it is of hedonic tone. The similarity of results in the present study and previous research suggests that icon scales may provide a convenient alternative to sensory scales in various modalities that are difficult to reproduce via current conventional computer interface technology.

Rat olfactory epithelial variations related to age and sex

Abstract Many previous studies suggest that olfactory epithelial structure and endocrine glandular activity are interdependent in animals as well as in man. Here we investigate variations in the rat olfactory epithelium as a function of age and sex. Specimens from prepuberal, postpuberal and old rats were examined by electron and light microscopy, and samples of the olfactory epithelium of estrous females were analyzed for the presence of oestrogen receptors. The results show important differences in the shape of the supporting cells in estrous females and old rats, as well as differences in the basal cell count, epithelium height, and nucleus concentration in the different groups of animals. These differences, together with the observed presence of oestrogen receptors, support the hypothesis that olfactory function and structure, and endocrine activity, are interdependent.

Determinants of perceived surface transparency in two-dimensional achromatic textured patterns.

Achromatic transparency in 2-D surfaces composed of three adjacent areas, one created from the others, occurs when in the created area it is possible to see the two colours of the adjacent areas. Displays with two white and black intersecting bars were produced to verify the possibility of perceiving transparency in the intersection area when this was subdivided into a different number of white and black diamonds. By increasing the spatial frequency of the elements in the intersection area we investigated the impression of transparency, and found that (i) the impression of transparency increases up to a spatial frequency of 10 cycles deg−1 and then levels off, (ii) there is a transition from a perception of transparency in which white and black are well discriminable to a perception in which a perceptually uniform grey is seen, (iii) the perception of transparency occurring when colours are discriminated seems consistent with Helsons area-luminance hypothesis [1964, in Adaptation Level Theory (New York: Harper & Row) pp 282 – 292], according to which the increase of spatial frequency determines the transition from the phenomenon of contrast to that of assimilation.

What is color

I want to begin by thanking each of you for attending. This session is very, very exciting to me, and I know that it willbe exciting and rewarding to you as well. We will begin by acknowledging Dr. All an Rodrigues and Dr. Danny Rich. We are the progenitors of this session. I believe that it is incumbent upon us to prepare ourselves, our companies or organizations for tomorrow by staying abreast of the state of-the-art, changes in technology, science, and trends, in our ever-changing world.