25 research outputs found
Illusory lightness in the Delboeuf Figure
No full textA white disk presented inside a small concentric circle (a display like Delboeuf figure) looks lighter than when inside a larger one. The magnitude of the effect was measured with 20 observers (10 women, 10 men; ages 19 to 26 years). The decrements in luminance of the disk inside the smaller circle, in order to match the lightness of the disk inside the larger circle, are reported for three different grey backgrounds and correspond to 9.13%, 10.33% and 10.46%
Measuring the meter: on the constancy of lightness scales seen against different backgrounds.
No full textThe constancy of a 16-step achromatic Munsell scale was tested with regards to background variations in two experiments. In experiment 1 three groups of observers were asked to find lightness matches for targets in simultaneous lightness displays by using a 16-step achromatic Munsell scale placed on a white, black, or white-black checkered background. In experiment 2, a yellow-blue checkered background and a green-red checkered background replaced Munsell scales on the black and on the white backgrounds. Significant effects of scale background on matches were found only in experiment 1, suggesting that background luminance is a crucial factor in the overall appearance of the scale. The lack of significant differences in experiment 2, however, may stand for an overall robustness of the scale with respect to background luminance changes occurring within certain luminance ranges
Lightness effects in Delboeuf and Ebbinghaus size-contrast illusions
No full textWe examined lightness effects observed in Delboeuf and Ebbinghaus size-contrast illusions. Results of four experiments are reported. Experiment 1 was conducted with Delboeuf-
like stimuli and shows that the disk that appears bigger appears either lighter or darker than
the disk that appears smaller, depending on the contrast polarity between disks and background.
Experiment 2 shows that the direction of these lightness effects is not influenced by the lumi-
nance of the size-contrast inducers. Experiment 3 shows that a similar lightness effect is also
observed in modified Ebbinghaus size-contrast displays. Experiment 4 tested the presence of the size-contrast illusion in the stimuli used in experiments 2 and 3
Visual similarity modulates visual size contrast.
No full textPerception is relational: object properties are perceived in comparison to the spatiotemporal context rather than absolutely. This principle predicts well known contrast effects: For instance, the same sphere will feel smaller after feeling a larger sphere and larger after feeling a smaller sphere (the Uznadze effect). In a series of experiments, we used a visual version of the Uznadze effect to test whether such contrast effects can be modulated by organizational factors, such as the similarity between the contrasting inducer stimulus and the contrasted induced stimulus. We report that this is indeed the case: size contrast is attenuated for inducer-inducing pairs having different 3D shapes, orientations, and even - surprisingly - color and lightness, in comparison to equivalent conditions where these features are the same. These findings complement related work in revealing basic mechanisms for fine-tuning local interactions in space-time in accord to the global stimulus context
Visual similarity modulates visual size contrast
No full textPerception is relational: object properties are perceived in comparison with their spatiotemporal context rather than absolutely. This principle predicts well known contrast effects: For instance, the same sphere will feel smaller after feeling a larger sphere and larger after feeling a smaller sphere (the Uznadze effect). In a series of experiments, we used a visual version of the Uznadze effect to test whether constrast effects can be modulated by higher-level factors, such as the similarity between the contrasting inducer stimulus and the contrasted induced stimulus. Our results suggest that the answer is positive for some dimensions of similarity, but not all. In particular, we report that size contrast is weaker for inducer-inducing pairs having the same shape but different colors, in comparison to the same color; for pairs having the same color, but different shape in comparison to the same shape; but that size constrast is unaffected by dissimilarity in orientation of gratings embedded in similar shapes. These findings complement related work in haptics (Kappers & Tiest, 2014) in suggesting that relational determination in perception can recruit high-level factors
Can music be figurative? Exploring the possibility of crossmodal similarities between music and visual arts
No full textAccording to both experimental research and common sense, classical music is a better fit for figurative art than jazz. We hypothesize that similar fits may reflect underlying crossmodal structural similarities between music and painting genres. We present two preliminary studies aimed at addressing our hypothesis. Experiment 1 tested the goodness of the fit between two music genres (classical and jazz) and two painting genres (figurative and abstract). Participants were presented with twenty sets of six paintings (three figurative, three abstract) viewed in combination with three sound conditions: 1) silence, 2) classical music, or 3) jazz. While figurative paintings scored higher aesthetic appreciation than abstract ones, a gender effect was also found: the aesthetic appreciation of paintings in male participants was modulated by music genre, whilst music genre did not affect the aesthetic appreciation in female participants. Our results support only in part the notion that classical music enhances the aesthetic appreciation of figurative art. Experiment 2 aimed at testing whether the conceptual categories ‘figurative’ and ‘abstract’ can be extended also to music. In session 1, participants were first asked to classify 30 paintings (10 abstract, 10 figurative, 10 ambiguous that could fit either category) as abstract or figurative and the to rate them for pleasantness; in session 2 participants were asked to classify 40 excerpts of music (20 classical, 20 jazz) as abstract or figurative and to rate them for pleasantness. Paintings which were clearly abstract or figurative were all classified accordingly, while the majority of ambiguous paintings were classified as abstract. Results also show a gender effect for painting’s pleasantness: female participants rated higher ambiguous and abstract paintings. More interestingly, results show an effect of music genre on classification, showing that it is possible to classify music as figurative or abstract, thus supporting the hypothesis of cross-modal similarities between the two sensory-different artistic expressions
The Stroop-matching task as a tool to study the correspondence effect using images of graspable and non-graspable objects
No full textThe Stroop-matching task is a variation of the Stroop task in which participants have to compare a Stroop stimulus attribute (color or word) to a second stimulus. The Stroop-matching response conflict (SMRC) represents an interference related to the processes involved in selection/execution of manual responses. In the present study, we developed a variation of the Stroop-matching task in which the Stroop stimuli were matched to graspable objects (a cup) with intact or broken handles laterally oriented (Experiment 1) or to colored bars laterally presented (Experiment 2). It allowed testing the presence of the correspondence effect for lateralized handles and bars and its possible influence on SMRC. Two different intervals (100 and 800 ms) were also included to investigate time modulations in behavioral performance (reaction time and accuracy). Fifty-five volunteers participated in the study. In both experiments, significant SMRC was found, but no interaction occurred between SMRC and correspondence effect, supporting that the hypothesis of different and relatively independent psychological mechanisms is at the basis of each effect. Because significant facilitation for ipsilateral motor responses (correspondence effect) occurred for graspable objects but not for lateralized bars, the attentional shift/spatial-coding view was not able to completely explain our data, and therefore, the grasping affordance hypothesis remained as the most plausible explanation. The time course of facilitation observed in the first experiment and by others indicates the importance of further studies to better understand the time dynamic of facilitation/inhibition of motor responses induced by graspable objects
Lightness effects observed in Delboeuf-like displays
No full text2009/2010La presente tesi di dottorato studia un effetto di bianchezza (colore acromatico di superficie) osservato nell’illusione di grandezza di Delboeuf. Nella sua forma classica l’illusione di Delboeuf (1865) è costituita da due dischi interni fisicamente uguali (target) circondati ciascuno da un cerchio concentrico (induttori) che differiscano tra loro in diametro. L’illusione di grandezza consiste nella differenza fenomenica di grandezza tra i due target uguali: il target circondotto dall’induttore piccolo appare più grande del target fisicamente identico ma circondato dall’induttore grande. Brigner (Brigner, W., L., 1980. Effect of perceived size upon perceived brightness. Perceptual and Motor Skills, 51,1331-1334.) fu il primo ad osservare un effetto di bianchezza nell’illusione di Delboeuf. In particolare, egli ha trovato che, a parità dalla direzione del rapporto di contrasto tra il target e lo sfondo, il target che appare più grande appare anche più scuro del target che appare più piccolo. Tuttavia, i risultati riportati recentemente da Zanuttini & Daneyko (Zanuttini L. & Daneyko O., 2010. Illusory lightness in the Delboeuf figure. Perceptual and Motor Skills, 111, 799-804) sono in contraddizione con quelli riportati da Brigner. In particolare, è stato osservato che quando i due target chiari sono visti sullo sfondo scuro, il target che appare più grande appare anche più chiaro. Gli obiettivi del presente studio sono: 1) verificare l'esistenza e la direzione dell’effetto di bianchezza osservato nell'’illusione di Delboeuf (esp. 1, cap. 1), e 2) testare il ruolo dei possibili variabili da cui il fenomeno potrebbe dipendere.
Per raggiungere il primo obiettivo, nell'esperimento 1 (cap. 1), ho usato due sfondi diversi, uno chiaro ed uno scuro, di modo che i target erano in un caso incrementi di luminanza rispetto allo sfondo, e nell’altro caso decrementi. Ho trovato che i risultati per target incrementali sono coerenti con quelli ottenuti nello studio precedente condotto da Zanuttini & Daneyko (2010): quando i due target sono uguali in luminanza, il target che appare più grande appare anche più chiaro. I target decrementali, invece, mostrano risultati opposti: quando i due target sono uguali in luminanza, il target che appare più grande appare più scuro, come riportato da Brigner per target decrementali.
Per raggiungere il secondo obiettivo, ho considerato tre fattori:
1) Il ruolo della luminanza degli induttori (i cerchi concentrici nell’illusione di Delboeuf; esp. 2, cap. 2; esp. 7, cap. 5);
2) Il ruolo della profondità percepita (alcuni studiosi ritengono che l’illusione di Delboeuf dipenda da indici impliciti di profondità; esperimenti 3 e 4, cap. 3);
3) il ruolo della grandezza relativa dei target (esp. 5 e 6, cap. 4; esp. 7, cap. 5; esp. 8, cap. 6)
In esperimento 2 ho testato l’effetto della luminanza degli induttori sulla differenza di bianchezza osservati in due dischi grigi posti come target nell’illusione di Delboeuf. Per fare previsioni sui risultati mi sono riferita a diversi gruppi di ipotesi, tra cui i modelli di integrazione dei margini per i colori acromatici (Rudd M. & Zemach I., 2004. Quantitative properties of achromatic color induction: An edge integration analysis. Vision Research, 44, 971-981), secondo cui ci dovrebbe essere un effetto maggiore di induzione nel gruppo induttore piccolo-target rispetto al gruppo induttore grande-target. Inoltre, la direzione degli effetti di induzione dovrebbero essere diversi se la luminanza dell’induttore è un incremento oppure un decremento rispetto alla luminanza del target. Dai risultati è emerso invece che la luminanza degli induttori non è una variabile che induce effetti significativi sulla bianchezza dei due target. Questo esito è stato confermato anche dai dati raccolti nell’esp. 7.
L’ipotesi sul possibile ruolo della profondità percepita sugli effetti di bianchezza osservati è ispirata dall’ipotesi che le illusioni di contrasto di dimensione sono determinate da fattori diversi, tra cui indici impliciti di profondità (Coren S. & Girgus J.S., 1975. A size illusion based upon a minimal interposition cue. Perception, 4, 251-254). In esp. 3 ho chiesto agli osservatori semplicemente di indicare quale target apparisse più vicino in configurazioni alla Delboeuf simili a quelli utilizzati nell’esp. 2. I risultati non hanno indicato alcuna differenza statisticamente significativa tra la scelta di quale target apparisse più vicino. Ho quindi proceduto con un secondo esperimento (esp. 4) usando configurazioni geometricamente più semplici: due target di uguale dimensione e di forma quadrata posti sopra uno sfondo chiaro oppure scuro. Ho creato la profondità percepita mediante presentazione stereoscopica. È risultato che il target che appare più distante appare anche più contrastato e più grande. Per verificare se la profondità percepita era la variabile che causava l’effetto di contrasto osservato in esp. 4, oppure se tale effetto era dovuto alla grandezza apparente del target (per la legge di Emmert, a parità di grandezza retinica, il target più distante appare anche più grande), ho condotto altri due esperimenti, la 5 e la 6, da cui sono emersi che i fattori in gioco non sono la profondità percepita, bensì sono in primo luogo il grado di appartenenza allo sfondo (esp. 5) e in secondo luogo la grandezza del target (esp. 6). I risultati sull’appartenenza percettiva sono in accordo con quelli riportati da Wolff (Wolff W., 1933. Concerning the contrast-causing effect of transformed colors. Psychologische Forschung, 18, 90–97) e da Kardos (Kardos L., 1934. Ding und Schatten [Object and shadow]. Zeitschrift für Psychologie, Erg. Bd, 23). Quelli riferenti alla grandezza sono invece una novità nel panorama degli studi sulla bianchezza delle superfici.
L’esperimento 7 è stato condotto per verificare se vi fosse una correlazione tra la modulazione dell’effetto di grandezza nell’illusione di Delboeuf e l’effetto di bianchezza ritrovata in quel tipo di display. La correlazione statistica non è emersa, e l’ipotesi è che l’effetto di incremento di contrasto rispetto allo sfondo per il target che appare più grande sia del tipo ‘o tutto o niente’: quando le condizioni sono presenti (stesso grado di appartenenza allo sfondo per i due target; diversa grandezza fenomenica), allora si verifica l’effetto e non è graduato dalla differenza apparente di grandezza dei target.
L’esperimento 8, infine, è stato condotto per verificare se il fenomeno esiste anche nell’illusione di Ebbinghaus, un’altra illusione ottico-geometrico di grandezza. Avendo ritrovato l’effetto di differenza di contrasto rispetto allo sfondo anche lì, e sebbene siano ancora necessari esperimenti parametrici per verificare l’estensione dell’illusione, penso di poter concludere dicendo che l’effetto di differenza di bianchezza tra target aventi la stessa luminanza, visti simultaneamente sopra uno sfondo chiaro oppure scuro, dipende dalla diversa grandezza relativa dei target, ma non dall’entità di tale differenza: il target più grande (fisicamente o solo fenomenicamente) apparirà più chiaro se i target sono un incremento di luminanza rispetto allo sfondo, e più scuro se sono un decremento.The present study is dedicated to a lightness effect (achromatic surface colour) observed in size-contrast displays. In one of its classic forms, the Delboeuf illusion (1865) consists of two inner disks (targets) equal in diameter, surrounded each by a concentric circle (inducers) that differ in diameter. The size-contrast illusion consists in the phenomenal size difference between the two targets: the target surrounded by the small inducer appears somewhat bigger than the identical target surrounded by the big inducer. Brigner (Brigner, W., L., 1980. Effect of perceived size upon perceived brightness. Perceptual and Motor Skills, 51, 1331-1334.) was the first to observe a lightness effect in Delboeuf’s size-contrast displays. In particular, he found that the target that appears bigger appears also darker than the target that appears smaller, independently from the contrast polarity between targets and background. However results reported recently by Zanuttini & Daneyko (Zanuttini L. & Daneyko O., 2010. Illusory lightness in the Delboeuf figure. Perceptual and Motor Skills, 111, 799-804) are in contradiction with those reported by Brigner. In particular, they showed that when two targets are luminance increments to the background, the target that appears bigger appears also lighter than the target that appears smaller. The goal of the present study was: 1) to verify the existence and the direction of the lightness effects observed within Delboeuf size-contrast displays, and 2) to explore and test the possible factors underlying the aforementioned lightness effects.
To achieve the first goal, in experiment 1 (Ch. 1) I have employed two backgrounds, one dark and one bright, so that targets were either luminance increments or decrements to the background. I found for increment targets results that are consistent with those obtained in the previous study by Zanuttini and Daneyko (2010): when a pair of targets in a stimulus have the same luminance, the target that appears bigger appears also lighter. Decrement targets show instead opposite results: when targets are equal in luminance, the target that appears bigger appears instead darker, and they are consistent with those reported by Brigner for decrement targets.
To achieve the second goal, I considered three factors:
1) The role played by the luminance of the inducers (outer concentric circles; exp. 2, Ch. 2; exp. 7, Ch. 5);
2) The role of perceived depth (some researchers hypothesized that Delboeuf’s size illusion depends on the presence of implicit depth indexes; experiments 3 e 4, Ch. 3);
3) The role of perceived size differences between targets. (exps. 5 e 6, Ch. 4; exp. 7, Ch. 5; exp. 8, Ch. 6).
In experiment 2 I tested the effect of inducer luminance on the lightness difference between the targets in Delboeuf-like displays. For the predictions on possible results I referred to several group of hypothesis, among which those derivable from edge intergation models for achromatic colour (Rudd M. & Zemach I., 2004. Quantitative properties of Achromatic color induction: An edge integration analysis. Vision Research, 44, 971-981), according to which a greater induction effect should be expected with small inducer+target than with big inducer+target. In addition, the direction of the induction effects should be different depending on whether the luminance of the inducers is an increment or a decrement with respect to the luminance of the target. Results showed instead that the luminance of the inducers is an ineffective variable for the lightness illusion observed within Delboeuf-like displays.
The hypothesis about the role of perceived depth on the observed lightness effects was inspired by those studies that suggested that size-contrast illusions are triggered by different mechanisms, including implicit depth clues (Coren S. & Girgus J. S., 1975. A size illusion based upon a minimal interposition cue. Perception, 4, 251-254). In exp. 3 I asked observers to choose which of two targets appeared closer in configurations similar to those employed in exp. 2. No significant result was found. Therefore I proceeded designing a new experiment with configurations geometrically simpler: two square targets of equal size seen against a dark or a bright background. I created an illusory depth differences between the two targets by employing stereograms viewed through a mirror stereoscope. Results were that the target that appeared more in depth appeared also more contrasted and bigger than the other target. In order to verify whether depth perception was causing the enhanced contrast effect with the background, or if the effects were due actually to a perceived size difference induced by stereopsis (according to Emmert’s law, with targets of equal angular size, the target that appears further away appears also bigger), I conducted experiments 5 and 6, from which it appears that the factors in play are not perceived depth, but first of all the degree of belongingness of a target to its background (exp. 5), and secondly the size difference between targets (exp. 6). The results regarding belongingness are in agreement with those reported by Wolff (Wolff W., 1933. Concerning the contrast-causing effect of Transformed colors. Psychologische Forschung, 18, 90-97) and Kardos (Kardos L., 1934. Ding und Schatten [ Object and shadow]. Zeitschrift für Psychologie, Erg. Bd, 23). Those which refer instead to size are new in the literature.
Experiment 7 was conducted to verify whether there is a correlation between how the size-contrast effect in Delboeuf-like displays is modulated by the size of the inducers, and the lightness effects observed in those displays. No correlation was found, so now my working hypothesis is that the effect of lightness differences observed in those displays is of the type all or none: when the conditions are favourable (same degree of belongingness to the background for the two targets; difference in apparent size), the target seen as bigger will also appear more contrasted to the background, but the enhanced contrast is not modulated by the magnitude of the size difference itself.
Finally, exp. 8 was conducted to verify whether the lightness effect exists also in Ebbinghaus’ illusion, another size geometric-optical illusion. Having found the effect also in the Ebbinghaus size-contrast illusion, and even though more parametric research is required to understand the extension of the illusion and its eventual modulations, I feel I can conclude that the effect of lightness difference between two targets of equal luminance presented simultaneously on a dark or bright background depends on the size difference between the two targets, but it is not modulated by the magnitude of such difference: the target that appears bigger (because it is somewhat bigger physically or only phenomenally) will appear lighter if the targets are luminance increments to the background, and darker if they are luminance decrements.XXIII Cicl
Temperature effect on stress-strain properties of dispersion-hardened crystalline materials with incoherent nanoparticles
No full textIn this paper, the mathematical simulation is used to study the effect from the size of incoherent nanoparticles on thermal strength of heterophase aluminum alloy in materials with the equal volume fraction of the strengthening phase. It is shown that during the deformation process, prismatic dislocation loops and dislocation dipoles contribute to the dislocation density. It is found that the behavior of the flow stress curves of materials with the equal volume fraction of strengthening particles depends on a combination of scale parameters of the strengthening phase at various deformation temperatures. The areas of strong and weak temperature dependence of the flow stress are identified
Stress-stain state of pipe made of copper-based alloy strengthened with incoherent nanoparticles
No full textThe approach which combines methods of crystal plasticity and deformable solid mechanics is used to explore the stress-strain state of a heavy-wall pipe made of dispersion-hardened Cu-based alloy and subjected to the uniform internal pressure. The distribution of the deformation and stress along the pipe wall is determined for various pipe geometry. The approximating equations are obtained to determine the yielding area and elastic and plastic strength limits
