Processing time of contour integration: the role of colour, contrast, and curvature

We investigated the temporal properties of the red - green, blue-yellow, and luminance mechanisms in a contour-integration task which required the linking of orientation across space to detect a 'path'. Reaction times were obtained for simple detection of the stimulus regardless of the presence of a path, and for path detection measured by a yes/no procedure with path and no-path stimuli randomly presented. Additional processing times for contour integration were calculated as the difference between reaction times for simple stimulus detection and path detection, and were measured as a function of stimulus contrast for straight and curved paths. We found that processing time shows effects not apparent in choice reaction-time measurements. (i) Processing time for curved paths is longer than for straight paths. (ii) For straight paths, the achromatic mechanism is faster than the two chromatic ones, with no difference between the red-green and blue-yellow mechanisms. For curved paths there is no difference in processing time between mechanisms. (iii) The extra processing time required to detect curved compared to straight paths is longest for the achromatic mechanism, and similar for the red - green and blue-yellow mechanisms. (iv) Detection of the absence of a path requires at least 50 ms of additional time independently of chromaticity, contrast, and path curvature. The significance of these differences and similarities between postreceptoral mechanisms is discussed.     

Role of chromaticity, contrast, and local orientation cues in the perception of density

We compared the role of the red-green, blue-yellow, and luminance post-receptoral mechanisms in the perception of density. The task requires the comparison of densities between two stimuli composed of oriented bandpass elements, pseudo-randomly scattered across an area of constant size. The perception of density differences was measured by a temporal 2AFC procedure for all pairs of mechanisms and for four possible densities. We found that stimuli of identical physical densities are not perceived equally: there is a consistent bias in favour of blue-yellow stimuli which are perceived as significantly more dense than red-green and achromatic stimuli. We considered three factors that could have differentially affected the density perception of blue-yellow stimuli: an increase in the perceived size of the individual blue-yellow elements, a perceived contrast difference, and the presence of local orientation cues. We found that the increased perceived density of the blue-yellow stimuli occurred despite the fact that there was no increase in perceived size of the individual elements, and remained despite corrections for the two other factors. We conclude that the significant increase in perceived density for the blue-yellow mechanism is a global effect, associated with a perceived colour 'melting' of the elements in the array. Our data were fitted with the occupancy model of Allik and Tuulmets (1991, Perception & Psychophysics 49 303-314) and we found that blue-yellow stimuli have a greater 'occupancy' than red-green or achromatic stimuli.     

Teaching Creative Writing Skills to Primary School Children in Hong Kong: Discordance Between the Views and Practices of Language Teachers

Although creativity has been valued in ancient and contemporary Chinese literature, the degree to which creativity is valued and incorporated into teaching by Chinese language teachers is not known. This information is important given that creativity has been increasingly recognized in the education literature as a component of effective writing. The purpose of this study was to compare the views of Chinese language teachers in Hong Kong about creativity and the acquisition of creative writing skills by primary school children, and their teaching practices. A total of 449 Chinese language teachers, employed at primary schools throughout Hong Kong completed a survey questionnaire. The 14‐item questionnaire focused on teachers' views of creativity, their perceptions of how to develop students' creativity, their awareness of creative writing strategies, and teaching practices related to creative writing. With respect to the definition of creativity, teachers identified imagination foremost, followed by inspiration, and original ideas. Teachers identified developing students' confidence, and providing an open atmosphere as essential means of fostering creativity. Despite the apparent value of creativity expressed by the teachers and their familiarity with methods for enhancing creativity, the majority reported using traditional methods of teaching writing. Strategies are recommended for reconciling this discrepancy, and promoting creative writing skills by primary school teachers in Hong Kong and other Chinese speaking societies.