Cognitive psychology 1

[5 abstracts]

1. Does physical contrast affect global induction in Agostini & Galmonte's reversed lightness-induction Necker cube?  
Galmonte A., Agostini T., Righi G.
First author's affiliation: Department of Psychology and Cultural Anthropology, Verona, Italy

In 2002 Agostini & Galmonte offered a reversed-contrast display where a gray target entirely surrounded by a black area appears darker than an identical gray target entirely surrounded by white. This effect can not be attributed to assimilation phenomena; moreover, it occurs because of higher-level grouping factors: when both higher-level factors and lower-level factors affect a configuration simultaneously, the former prevail. Hence, the authors showed that the lightness induction determined by perceptual belongingness prevails against retinal lateral inhibition. The purpose of this work was to investigate whether the lightness induction produced by global grouping factors does change as a function of the physical contrast between induced and inducing elements. We systematically manipulated the relative physical contrast among the regions forming the original Agostini & Galmonte display. Observers had to judge the lightness of both the inducing and induced element on a Munsell Scale. From the results we can conclude that: 1. the global induction overcomes local induction for all the tested physical contrasts, 2. it is stronger for decrements, 3. the amount of the global induction does not depend on the size of physical contrast, 4. the global induction seems to be modulated by the physical contrast of increments only.

2. Distance and orientation in suspect identification under poor illumination conditions: Simulation of a real case  
Agostini T., Righi G., Galmonte A.
First author's affiliation: University of Trieste, Trieste, Italy

Visual perception plays a crucial role within witness psychology. It is not unusual that the accused are found guilty only on the basis of eyewitness identification. The Italian national TV asked us to reproduce the visual conditions under which a witness was in at a mafia murder, and to run an experiment to test whether in these conditions she could have unambiguously identified the killer. A group of 72 observers has been tested. Two variables were manipulated: distance (killer-observer: 6 or 16 meters) and orientation (killer viewed frontally, 45 degrees left, 45 degrees right). Illumination conditions were controlled (low intensity illumination). The experiment was run in 2 different days. In the fist day, each observer (12 for each condition) viewed the killer for 1.5 seconds. Four days later they were asked to identify the killer among 5 look-alike persons in a simultaneous line-up. Results show that in our stimulation conditions (low intensity illumination) both correct and incorrect identifications were not statistically different from chance, independently from both viewing distance and orientation.

3. Voluntary attention increases the phenomenal length of briefly flashed lines  [presentation, ppt, 487 kB]
Masin S. C.
Università di Padova, Padova, Italy

In 1956, Fraisse, Ehrlich, and Vurpillot found that subjects judged that lines were longer when voluntary attention was focused on the lines than when attention was distracted from the lines. There have been many attempts to repeat these results, but so far none has been able to ascertain whether the effect of attention on reported line length was a phenomenal effect. In the present study, 46 subjects were shown stimuli consisting of pairs of horizontal or vertical briefly flashed lines with a fixation cross placed equidistant between the lines, far from each of the lines. A change in colour of one arm of the cross was used as a cue to focus the subject's voluntary attention on one line. The results showed that attention increased the judged length of the attended lines. Since this effect of attention also occurred when the subjects were absolutely certain that they saw that the stimulus lines differed in length, this effect indicates that attention increased the phenomenal length of the attended lines. This lengthening was quite small: it involved a maximum mean increase of about 0.15 in the probability of responding that the attended line was longer. This effect occurred in the horizontal dimension and was almost absent in the vertical dimension. In agreement with data indicating that flashed lines expand phenomenally by activating motion detectors and that focused attention makes neural motion responses increase in amplitude, the present results suggest that focused attention makes attended lines look longer because it makes these lines expand phenomenally more rapidly.

4. A comparison of methods for estimating the capacity of visual working memory: Examination of encoding limitations  [presentation, ppt, 168 kB]
Švegar D., Domijan D.
First author's affiliation: Department of Psychology, University of Rijeka, Rijeka, Croatia

The primary goal of the present study was to answer the following question: is visual working memory capacity indeed extremely limited, or it is erroneously underestimated due to inadequate encoding of stimuli? Visual working memory capacity is estimated by a procedure known as change-detection paradigm, in which two sets of stimuli are presented. These two displays are separated by an interstimulus interval, during which a change may occur, usually on one of the stimuli. Participants' task is to answer if change had occurred or not, and the memory capacity is then estimated through analyses of their performance. In the majority of recent studies it was found that the memory capacity is limited to three or four objects. Although there is a consensus regarding the capacity limitation, all previous studies are based on the same procedure, in which it is uncertain that visual objects are adequately encoded into working memory. In order to assure their adequate encoding, we constructed a new procedure, in which stimuli are presented successively in the initial stage. That experimental condition was compared to a condition using classical change-detection paradigm, in which objects are initially presented simultaneously. Besides the initial presentation, testing of memory was also varied: in one condition memory was tested with partial test-displays, while in the other, full test-displays were applied. Thus, a 2 x 2 experimental design was used. Analyses have shown that the main effect of the type of presentation was not significant, and it can therefore be concluded that visual working memory capacity was not underestimated due to encoding limitations in previous studies. The main effect of test display type and the interaction were both also insignificant.

5. Colour effect on picture recognition memory  [presentation, pps, 1122 kB]
Nakic S., Pavela I.
First author's affiliation: University hospital "Sestre milosrdnice", Zagreb, Croatia

Different features of pictures can be used as recognition clues. Previous studies have shown that colour is one of them. However, it is still unclear whether enhanced recognition memory by colours is due to the distinctiveness of features highlighted by colours (sensory facilitation), or it is due to the colour representation in memory (cognitive facilitation). In the last case, unnaturally coloured pictures would be more difficult to memorize. This study was conducted to investigate colour effects on picture recognition memory. Colour diagnosticity was manipulated by using pictures in two colours modes: naturally and unnaturally coloured pictures, as well as black and white pictures. Since there were three different versions of picture in the encoding phase and three in the recognition phase, there were nine possible combinations of encoding and recognizing pictures. There were three groups of participants who were exposed to three different combinations of encoding and recognizing pictures. Accuracy and recognition time were measured. Results showed strong encoding-specificity effect (better picture recognition in the same version as in the study phase), as well as improved recognition memory by both colour modes. This indicates that colour improves recognition memory through sensory facilitation, not by colour representation in memory. Moreover, recognizing pictures in black and white includes different mechanisms from those involved in recognizing coloured pictures. Furthermore, recognition time was the longest for black and white pictures and the shortest for naturally coloured ones, which suggests that recognition time depends on the fact that colour is a part of the identity of picture stimuli.