Biomedical subjects

M Liinasuo

Publications and source records attributed to M Liinasuo.

5 recordsLinked to original sources

PubMed2000

Neon colour spreading in three-dimensional illusory objects in humans.

We studied whether neon spreading can be induced within three-dimensional illusory triangles. Kanizsa triangles were induced by black pacman disks consisting of red sectors with curved sides. Viewing our stimuli monocularly produced two-dimensional illusory contours and surfaces as well as neon spreading in each figure. Triangles appeared concave or convex under stereoscopical viewing. Neon colour spreading was induced within illusory figures bending in three-dimensional space, suggesting that neural contour completion and surface filling-in interact across depth. Surprisingly, neon spreading was induced above the intervening surface even when the inducers were below the surface. Neon colour and illusory configuration were preserved behind the intervening surface only when it appeared transparent.

Adolescent↗

PubMed1998

Three-dimensionally slanted illusory contours capture stereopsis.

In stereo capture a stereogram of a crossed illusory figure pulls a texture bounded by the illusory contours to the same depth plane with the illusory figure. We investigated whether three-dimensionally curved and slanted illusory figures could capture a repeating background texture. According to results, stereoscopic capture was perceived when a disparate illusory contour was slanted provided that the period of the background texture was consistent with the three-dimensional geometry of the illusory surface. We suggest that stereo capture is actually induced by disparate rows of points defined by vertical cut-out sectors and the induced disparity spread is constrained by illusory contours and possible discrete matches of the background texture.

Adult↗

PubMed1997

Effects of spatial configuration and number of fixations on Kanizsa triangle detection.

PURPOSE: Illusory figures, created by the visual system between visualizing real objects, are probably caused by processes designed to segregate objects from background. Support ratio--that is, the ratio between the physically specified and total triangle side length--has been suggested to be the main spatial determinant for suprathreshold perception of a Kanizsa-type illusion. To test this scale invariance hypothesis at threshold, illusory figure perception was studied by determining the effects of inducer size and distance at various exposure durations and fixation strategies on the frequency of seeing (FoS) an illusory Kanizsa triangle. METHODS: The effect of various support ratios was studied in the first experiment by varying the intercenter distance between constant-size inducers viewed at various distances. In the second experiment, the effects of various exposure durations and fixation strategies were investigated; and the third experiment repeated the second one, with backward masking to control the processing time. In the fourth experiment, the magnification of the stimulus configuration was varied, with a support ratio that had yielded 100% FoS in the first experiment, to study the range of scale invariance in illusory figure perception. RESULTS: The support ratio was the main determinant for the perception of an illusory figure at various inducer sizes, exposure durations, and masking conditions when fixation was steady; FoS always increased from 0% to 100% with the support ratio of 0.30 to 0.37. However, free viewing, with and without masking, resulted in 100% illusory figure perception at all support ratios tested. Furthermore, when fixation was steady and support ratio and exposure duration were held constant, stimulus magnification reduced FoS from 100% to 0% at the smallest and largest stimulus sizes. CONCLUSIONS: The support ratio seems to be the main spatial determinant for illusory figure perception. However, scale invariance in Kanizsa triangle perception broke down in the smallest and largest configurations, probably because of the limitations of visual acuity and spatial integration, respectively. Integration of information from several fixations enhances FoS at small support ratios, emphasizing the importance of the binding process between separate fixations for illusory figure perception.

Adult↗

PubMed1994

Three-dimensional illusory objects produced by rotation in depth.

Rotation of a Kanizsa triangle in depth around its vertical axis causes a perception of a three-dimensional object with a flat, rigid illusory triangle between the inducing discs. When the inducing discs of a Kanizsa triangle were made thicker, the illusory triangle between the discs also became thicker. In the experiments both computer animation and real inducers made of plastic were used. The method promoted border perception in a three-dimensional illusory figure. We suggest that the perception of three-dimensional illusory objects is due to a process which is also used in the perception of real three-dimensional objects.

Adult↗

PubMed1993

Spatial and temporal properties of illusory figures.

The best known example of illusory figures is the Kanizsa triangle consisting of three disks with a sector removed. The disks and sectors are arranged so that they form the corners of a triangle. Although the sides of the triangle are not physically present, they are clearly visible to the observer. In this study the effect of sequential presentation of the inducing disks on an illusory (Kanizsa) triangle was investigated. The task of each subject was to find, by the method of adjustment, the longest critical duration that allowed perception of the illusory triangle produced by presenting the three inducing disks sequentially. We varied the sizes and/or separations of disks. An illusory triangle produced by flashing the three inducing disks simultaneously for 33 msec served as a comparison stimulus. Our experiments showed that increasing the inducing disk size or reducing the inter-disk distance increased critical duration. The result means that the shorter the illusory contour to be induced the longer the critical duration and vice versa. Thus, if the inductive disks are less separated in space they can be more separated in time and vice versa. These findings seem to agree with the suggestion that illusory contours emerge from the synchronization of gamma-waves emitted by the neurons in the visual cortex.

Adult↗