Bielevičius, Arūnas

The visual system overestimates the length of structured contours relative to adjacent empty intervals of the same physical size. This study examined whether apparent-length expansion occurs across isolated contour parts as well as complete objects, and whether the expansion of the whole can be predicted from that of its components. Observers matched the perceived horizontal extent of complete pentagons, incomplete pentagons with one or two missing segments, isolated apices, pedestals, parallel line pairs, and rectangles using an adjustment method. All stimulus types produced consistent positive mean errors, indicating robust apparent-length expansion across a wide range of contour configurations. The magnitude of expansion depended on contour geometry rather than on physical size alone: removing contour segments did not reduce expansion and, in some cases, increased it. Isolated parts produced expansion effects comparable to or larger than those of the corresponding whole pentagons, but the sum of part effects did not predict the whole-object effect. These findings support a configuration-dependent account of apparent-length expansion and appear inconsistent with simple part-based additivity.

Parazitologijos mokslas Lietuvoje turi ilgą ir reikšmingą istoriją, glaudžiai susijusią su šalies gamtos ypatumais, žemės ūkio tradicijomis ir visuomenės sveikatos poreikiais. Šiandienos pasaulyje, susiduriant su klimato kaita, globalizacija ir naujų infekcinių ligų atsiradimu, parazitologijos reikšmė Lietuvoje dar labiau padidėja. Klimato ir geografinės sąlygos sudaro palankias sąlygas veistis Įvairiems parazitams, plėstis parazitų pernešėjų arealams, o tai kelia naujus iššūkius visuomenės sveikatai ir biologinei Įvairovei. Parazitologijos studijų dalykas mūsų Universitete nuėjo ilgą evoliucijos kelią, keitėsi studijų programos, mokymo priemonės, gilėjo patirtis. Ši patirtis (buvusių ir esamų) Biologinių sistemų ir genetinių tyrimų instituto darbuotojų perduodama Jums, mieli skaitytojai. Mūsų parengta mokomoji knyga skiriama pirmojo kurso studentams, studijuojantiems biomedicinos mokslus - mediciną, odontologiją, burnos higieną, slaugą ir visuomenės sveikatą. Leidinyje pateikiamas parazitologijos kursas, apimantis svarbiausius žmogaus parazitus, jų morfologiją, sukeliamas ligas, diagnostikos principus ir profilaktikos priemones. Šias teorines žinias padės įtvirtinti praktikos darbai. Kiekvieno praktikos darbo pabaigoje pateikiami saviruošos klausimai, skirti suprasti ir Įsiminti praktikos darbų metu analizuojamus parazitus. Tikimės, kad šis leidinys bus naudingas ne tik pratybų metu, bet ir savarankiškai mokantis, ruošiantis atsiskaitymams arba rengiant baigiamuosius darbus.

This study examined the accuracy of locating the geometric center of visual stimuli, represented by different parts of the contour, using eye-tracking equipment. Two methods of stimulus representation were employed. In one, geometric shapes – rectangles, rhombuses, pentagons, and horizontal bars – were composed of lines 2 px thick (1 px = 1.8 arcmin) with a brightness of 300 cd/m ² on a grey background of 25 cd/m ². In the other, the shapes were marked by bright spots 5 px in diameter positioned at the corners. The experiment included three sizes of shapes: large (800 × 400px or 800 × 800 px), medium (400 × 400 px), and small (200 × 400 px or 200 × 200 px). Method Stimuli were presented singly in random order on a 117 cm diagonal, 1920 × 1080 px resolution “Samsung LE 46 B 652” screen. The participant was seated 1 m from the screen, with head movements stabilized using a mount. Eye movement tracking, stimulus presentation, and data collection were performed using the ViewPoint PC-60 system (Arrington Research, Inc.). After calibration, the participant viewed each stimulus for 6 seconds, during which their eye movements were tracked and displayed in real-time. Seven university students, with an average age of 26 years, took part in the study. Analysis Data from the final second of each of the 11 experimental runs were collected to estimate the perceived location of the centroid. Analyses and visualizations were carried out using Python (custom scripts) and MS Excel. According to the average data of all observers, differences in the representation of geometric shapes did not significantly affect the accuracy of center finding. For large rhombuses represented by lines, compared with same figures predicted by corners, the center difference in the X axis was 14 pixels, and along the Y axis – just 3 pixels; for medium shapes, the X difference was 44 pixels, Y – 13 pixels; for small shapes, the X difference was –31 pixels, Y – 4 pixels, for large rectangle X – 19, Y – -21; medium X – -11, Y – -3; small X – -10, Y – 40, for large pentagon X – 35, Y – 19; medium X – -21, Y – -8, small X – -8, Y – 3, for large horizontal bar X – -11, Y – 1, medium X – -82, Y – -10, small X – 43, Y – -3. The variations in perceived locations of the geometric centers of differently depicted shapes were not statistically significant.

This study investigates the visual phenomenon of increasing stimulus size [Bertulis & Bielevicius. Expansion of perceived size. J. Perception, 2025]. In psychophysical experiments, observers adjusted the test distance to match the length of the entire stimulus— the pentagon—and its components: the apex and the rectangular segment, which can be called the pedestal, both when separated and combined. The shape of the pentagon changed during presentations due to three simultaneous variables: a) the length of the apex gradually increased from 30 to 180 arc minutes, b) the horizontal edges of the pentagon decreased from 150 to 0 arc minutes; and c) the apex angle narrowed from 100 to 23 degrees, while the pentagon’s length and height remained constant at 180 and 72 arc minutes, respectively. Based on the averages of the experimental results, the pentagonal-shaped stimulus demonstrated an expansion effect, which, due to shape changes, ranged from 2 to 19 arc minutes. For the isolated apex with increased length and narrowed opening angle, expansion values were higher and, ranging from 10 to 33 arc minutes, showed a consistent upward trend without reaching a peak. In the pentagon’s structure, the apex with similar shape and size dynamics displayed a different expansion profile. The expansion value gradually increased from about 9 to 35 arc minutes (its maximum), then decreased to 30 and 19 arc minutes. Similarly, the pedestal displayed different patterns when viewed as a separate object and as part of the pentagon. The isolated pedestals showed expansion (7 to 30 arc min) throughout. Inside the pentagon, narrow pedestals (30, 60 arc min) did not even exhibit expansion and instead showed a negative error sign. Wider pedestals produced relatively weak expansion, peaking at 8 arc minutes before decreasing to 1.5 arc minutes. The combined curves of the isolated apex and pedestal did not match the experimental curve of the whole pentagon. Based on the data, the perceived shape seems to be a key factor in determining perceived size and, therefore, the expansion effect. During the visual size-matching process, the spatial proportions within the perceived shape are likely to change when combined with another shape, even though the geometry remains unchanged. The representation of a shape (such as a pentagon) in higher neural networks is not simply a sum of its parts’ representations (apex and pedestal).

The study builds upon previous research on the perceived size of visual objects of various shapes compared to an empty spatial interval. In psychophysical experiments using the size-matching procedure, the effect of overestimating the relative size of an object (relative to an equivalent empty space) was consistently observed when testing visual objects, such as rectangles, circles, ellipses, rhombuses, and triangles, in both filled and empty formats. The strength of the illusion did not depend on whether the shapes were filled or not, but rather it varied with the shape itself. Objects with open contours, such as angles of different orientations and narrow stimuli like straight, tangled, defocused, and divided lines, all produced the expansion effect. The overestimation manifested during testing stimuli of various contour types, including spatial contrast of luminance, colour, and texture, as well as those determined by perceptual grouping and illusory outlines of Kanizsa and Oppel-Kundt versions. Finally, the expansion effect was found to be more pronounced with increasing length and height of the stimuli. The data supported the assumption that the object contour is the primary inducer of perceived size expansion and that the overestimation effect is a regular phenomenon rather than an incidental event.

We present a post-hoc analysis examining whether repeated trials and multiple sessions affect the measured strength of two length illusions, Oppel-Kundt (O-K) and Müller-Lyer (M-L), as well as a non-illusory control stimulus. Data were taken from earlier studies in which participants adjusted a variable segment to match a reference segment. Short sessions featured five trials per figure, whereas extended sessions contained 24 or 26 trials for O-K and M-L. Linear mixed-effects models tested how trial number, session number, initial interval length, and figure subtype influenced illusion magnitude. O-K illusion magnitude tended to decline across sessions in the extended sessions, although individual observers displayed varying trends—some increased, others decreased. M-L illusions did not show the pronounced adaptation reported in previous work. These findings highlight the need to manage repeated presentations: controlling viewing durations, inter-session intervals, and participant strategies can help limit adaptation. Methodologically, mixing different stimuli, randomizing key parameters, and scheduling breaks appear to yield more stable measurements of illusion magnitudes.

In psychophysical experiments on a monitor screen, a subjective contour of a rectangular shape was formed by a random dot pattern drifting against a background of static random dots. Bidirectional drifting: divergence, and convergence were applied within the rectangle area. The aim was to answer whether the direction of movement selectively influences the perceived relative length of the motion-defined shape. Subjects judged the relative extension of the reference stimulus by adjusting the perceptually equal length of the test gap. It was demonstrated that dots moving horizontally toward the stimulus periphery and tangentially approaching the rectangle edges in the case of divergence caused an overestimation of the rectangle length. The positive errors of the subjects indicated that the rectangle edges perceptually shifted outward. The shift values were about the same for shorter and middle rectangles but lower for longer ones. The size expansion effect appeared to reduce at a certain motion distance. When convergence was tested, dots escaping the rectangle edges and drifting toward the stimulus center caused relatively low error values that continuously declined with stimulus length. There were even negative signs of errors for six subjects out of eight for longer rectangles. The effect of expansion was questionable. Consequently, the approaching and escaping dots don’t act the same way on the positions of the subjective contour. But was the expansion produced by the divergent motion of the same origin as the expansion of stimuli outlined by a static spatial contrast in luminance, color, or texture, and defined by perceptual grouping and the Kanizsa contours (Bielevicius, et al., 2023)? To compare the two manifestations of expansion, the control stimuli were formed of static lines and exposed on the same background of random dots in the present study. The divergently drifting dots were still presented within the rectangle area. The rectangle sizes were the same as before that. Such stimuli caused overestimation errors exceeding those of the motion defined contours. In addition, the expansion strengthened, while not decreasing, with an increase in the length of the stimulus. As a result, for long stimuli, the expansion of the static contour became two to three times higher than that of the motion-defined contour. The size expansion effects for static and motion-defined contours may have different neural origins.

Aim: This psychophysical study utilizes eye-tracking technology to investigate gaze patterns as participants evaluate the lengths of various geometric shapes. Methods: Six geometric shapes were used as stimuli: rectangle, ellipse, triangle, line, rectangle with concave lateral edges, and two crossed segments. Each shape measured 8.2 × 2.7 arc minutes and was presented alongside a reference spot with a diameter of 0.27 arc minutes. Stimuli were displayed in two sizes: the larger size had a reference distance of 11.9 arc minutes, and the smaller size had a reference distance of 5.1 arc minutes, both defined by the spot. Each stimulus was displayed for 1.5 seconds, during which participants judged whether the left or right segment of the shape was longer. Participants used a computer mouse to indicate their responses: the left mouse button for “left side longer” and the right mouse button for “right side longer.” All tests were conducted monocularly in a darkened room. Eye movements of the 10 participants were recorded throughout the experiment, with data processed and visualized using MS Excel and a proprietary author’s software. Results: The data revealed distinct eye fixation patterns influenced by stimulus size and shape. For larger stimuli such as rectangles and ellipses, participants’ fixations occurred approximately 7 arc minutes from the center, directed towards the reference spot. For triangles positioned peripherally, fixations shifted further, averaging 8.3 arc minutes. Smaller stimuli, in contrast, elicited fixations closer to the center: lines prompted a fixation shift of only 1.6 arc minutes, rectangles with concave edges 1 arc minute, and two crossed segments demonstrated the smallest shift at 0.8 arc minutes. Conclusions: Observers’ gaze points were either centered on the midpoint of the comparison distance or near the center of larger stimuli. For smaller stimuli, fixation points tended to cluster close to the center.

Introduction. The present study focuses on the expansion effect of the relative size of isolated stimulus parts like angles, broken lines, and short stripes. Subjects (M, N, O, L, Ë, A, B, R, P, H, K, and Г) matched the test distance to the referential stimuli length by adjusting the position of the terminal spot. The testing distance was limited to the terminal spot and the vertex or sideline of a referential figure. The starting referential stimulus was the contour pentagon (facsimile in Fig. 1). Lines and their combinations were removed from the pentagon to show separate parts. The background's luminance and the stimuli lines were 0.01 cd/m2 and 23 cd/m2 , respectively. Results. A. All modified stimuli caused the effect of length expansion, which did not significantly differ in strength from the entire pentagon (13.8 arc min; Fig 1 medial section). The illusion grew slightly from 13.8 to 15.7 arc min P = 0.397 (Welch's t-test) in the stimulus without a lower horizontal line and from 13.8 to 15.2 arc min P = 0.561 in that without the bottom two lines. B. An angle, a pair of wings (Fig. 1 right section) was twice shorter than the pentagon, but the illusion, on the contrary, increased from 13.8 to 16.9 arc min P = 0.176. C. When the open rectangle was presented (left section in Fig.1), the illusion strength did not change: 13.8 → 13.1 arc min P = 0.716, regardless of the stimulus change in spatial structure. D. When the vertical segment was removed from the open rectangle, and two parallel horizontal lines remained, the illusion increased: 13.1 → 17.4 arc min P = 0.015. E. If two vertical segments were added to the two horizontal lines to make the stimulus a rectangle, the strength of the illusion slightly decreased: 17.4 → 15.5 arc min P = 0.278. Conclusions. Components of a visual stimulus presented as isolated should be considered full-fledged objects in the size comparison procedure. The individual shape of an object determines the strength of the size expansion. A sum of the expansions of the size of stimulus parts significantly differs from the expansion of the whole. The present experimental data favor the functional relationships of the contour segments forming the shape, not the integration of reactions to each segment during the relative size estimation.

Viena didžiausių evoliucijos sėkmės istorijų yra žmogus, kurio pagrindas - ląstelė. Kiekviena atskira ląstelė turi 3,5 milijardų metų patirtį, todėl net mažiausi aplinkos ar vidaus pokyčiai verčia ją sureaguoti, prisitaikyti ir išgyventi. Daugialąsčių organizmų ląstelių tarpusavio bendravimo patirtis, palyginti su atskira ląstele, yra tik 600 milijonų metų. Gal todėl žmogaus ląstelės į pakitusią aplinką kartais sureaguoja mums nesuprantamu būdu. Norėdama suprasti ir atsakyti į šiuos ar panašius klausimus žmonija kaupia patirtį: eksperimentuoja, mokosi iš klaidų, kuria naujus tyrimus. Ši knyga yra mažas pasidalijimas patirtimi, kokiais būdais galima pažinti ląstelę, ir šie būdai autoriams yra vieni įdomiausių. Ši Lietuvos sveikatos mokslų universiteto Biologinių sistemų ir genetinių tyrimų instituto dėstytojų parengta mokomoji knyga skiriama 1 kurso studentams, studijuojantiems biomedicinos mokslus: mediciną, odontologiją, medicininę ir veterinarinę genetiką, žmogaus ir gyvūnų sąveiką, slaugą bei visuomenės sveikatą. Leidinyje pateikiamos atitinkamos teorinės žinios, kurias įsisavinti padės praktikos darbai. Kiekvieno praktikos darbo pabaigoje sudaryti saviruošos klausimai padės suprasti ir įsiminti praktikos darbų metu analizuojamas ląstelių struktūras, funkcijas, ląstelėse vykstančius procesus ir ląstelių analizės metodus. Autoriai dėkoja visiems instituto dėstytojams ir laborantams, padėjusiems parengti eksperimentus, pritaikyti juos studijoms ir iškristalizuoti jų kokybę. Dėkojame darbuotojams Irenai Lašienei, Silvijai Malčiauskienei, Mildai Kaliasienei, Sabinai Greblikienei, Astai Raskilienei, Jelenai Loginovich, Linai Mickienei ir Algiui Bertuliui, prisidėjusiems rengiant leidinį. Ypatinga padėka skiriama mokomosios knygos recenzentams doc. dr. Jolitai Palubinskienei ir prof. Rimantui Daugelavičiui, suteikusiems galimybę savo pastabomis, patarimais ir įžvalgomis pakelti leidinio turinį į aukštesnį kokybinį lygmenį. Kaip ir kiekvienas kūrinys, jis nėra tobulas, todėl iš anksto dėkojame skaitytojams, padėsiantiems rasti netikslumų ar trūkumų.