A selection from Stockholm University publication database

• Något om psykofysiken och dess utvecklingi Stockholm... ur mitt perspektiv

  2020. Åke Hellström. Historien om svensk psykologisk forskning, 97-106

  Chapter

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• Sensation weighting in duration discrimination

  2020. Åke Hellström, Geoffrey R. Patching, Thomas H. Rammsayer. Attention, Perception & Psychophysics 82, 3196-3220

  Article

  Stimulus discriminability is often assessed by comparisons of two successive stimuli: a fixed standard (St) and a varied comparison stimulus (Co). Hellstrom's sensation weighting (SW) model describes the subjective difference between St and Co as a difference between two weighted compounds, each comprising a stimulus and its internal reference level (ReL). The presentation order of St and Co has two important effects: Relative overestimation of one stimulus is caused by perceptual time-order errors (TOEs), as well as by judgment biases. Also, sensitivity to changes in Co tends to differ between orders StCo and CoSt: the Type B effect. In three duration discrimination experiments, difference limens (DLs) were estimated by an adaptive staircase method. The SW model was adapted for modeling of DLs generated with this method. In Experiments 1 and 2, St durations were 100, 215, 464, and 1,000 ms in separate blocks. TOEs and Type B effects were assessed with univariate and multivariate analyses, and were well accounted for by the SW model, suggesting that the two effects are closely related, as this model predicts. With short St durations, lower DLs were found with the order CoSt than with StCo, challenging alternative models. In Experiment 3, St durations of 100 and 215 ms, or 464 and 1,000 ms, were intermixed within a block. From the SW model this was predicted to shift the ReL for the first-presented interval, thereby also shifting the TOE. This prediction was confirmed, strengthening the SW model's account of the comparison of stimulus magnitudes.

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• Conceptual elaboration versus direct lexical access in WAIS-similarities

  2018. Sven-Erik Fernaeus, Åke Hellström. Aging, Neuropsychology and Cognition 25 (6), 893-903

  Article

  Wechsler Adult Intelligence Scale (WAIS) subscale Similarities have been classified as a test of either verbal comprehension or of inductive reasoning. The reason may be that items divide into two categories. We tested the hypothesis of heterogeneity of items in WAIS-Similarities. Consecutive patients at a memory clinic and healthy controls participated in the study. White-matter hyperintensities (WMHs) and normalized temporal lobe volumes were measured based on Magnetic resonance Imaging (MRI), and tests of verbal memory and attention were used in addition to WAIS-Similarities to collect behavioural data. Factor analysis supported the hypothesis that two factors are involved in the performance of WAIS-similarities: (1) semiautomatic lexical access and (2) conceptual elaboration. These factors were highly correlated but provided discriminative diagnostic information: In logistic regression analyses, scores of the lexical access factor and of the conceptual elaboration factor discriminated patients with mild cognitive impairment from Alzheimer’s disease patients and from healthy controls, respectively. High scores of WMH, indicating periventricular white-matter lesions, predicted factor scores of direct lexical access but not those of conceptual elaboration, which were predicted only by medial and lateral temporal lobe volumes.

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• Effects of sensitivity, bias, and stimulus presentation order in comparative discrimination of interval durations

  2018. Åke Hellström, Thomas Rammsayer. Fechner Day 2018, 266-271

  Conference

  According to the sensation weighting model (SWM), stimulus magnitude level dependent time-order errors (TOEs) in stimulus comparison arise from uneven stimulus weighting, levered by asymmetry of an internal reference level; the weighting also causes discriminability to depend on the presentation order of standard (St) and comparison stimulus (Co) (the Type B effect). Both of these effects, as well as judgment bias, determine the measured difference limen (DL). In two duration discrimination experiments, these contributions to the DL were explored, using an adaptive staircase method. The compared intervals were filled auditory or empty visual. The interstimulus interval was 900 ms and the St duration 100, 215, 464, or 1000 ms in a blocked design. In univariate as well as multivariate analyses, the SWM’s predictions were confirmed on the individual level, and the contributions of sensitivity, bias, and weighting in building the DL were assessed.

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• Interrater Reliability of Psychopathy Checklist–Revised

  2018. Anna M. Dåderman, Åke Hellström. Criminal justice and behavior 45 (2), 234-263

  Article

  Scores from the Psychopathy Checklist–Revised (PCL-R) are used to support decisions regarding personal liberty. In our study, performed in an applied forensic psychiatric setting, intraclass correlation coefficients (ICC) for absolute agreement, single rater (ICC_A1) were .89 for the total score, .82 for Factor 1, .88 for Factor 2, and .78 to .86 for the four facets. These results stand in contrast to lower reliabilities found in a majority of field studies. Disagreement among raters made a low contribution (0%-5%) to variability of scores on the total score, factor, and facet level. For individual items, ICC_A1 varied from .38 to .94, with >.80 for seven of the 20 items. Items 17 (“Many short-term marital relationships”) and 19 (“Revocation of conditional release”) showed very low reliabilities (.38 and .43, respectively). The importance of knowledge about factors that can affect scoring of forensic instruments (e.g., education, training, experience, motivation, raters’ personality, and quality of file data) is emphasized.

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• Dyslexia Prevalence in Forensic Psychiatric Patients

  2015. Heidi Selenius, Åke Hellström. Psychiatry, Psychology and Law 22 (4), 586-598

  Article

  Research on dyslexia in forensic psychiatric patients is limited, and therefore one aim of this study was to assess the prevalence of dyslexia in a sample of forensic psychiatric patients by using different criteria. Another aim was to investigate how phonological-processing skills in these patients might be related to disadvantageous background factors and poor reading habits. Forensic psychiatric patients performed reading, writing and intelligence tests, as well as a battery of phonological processing tasks. They were also interviewed about reading habits and literacy conditions in their childhood homes. Data regarding the patients’ dyslexia diagnoses and backgrounds were collected from forensic psychiatric investigations and patient records. The results showed that 11–53% of the patients met the discrepancy criteria for dyslexia, whereas 50% fulfilled the phonological core deficit criterion. Neither disadvantageous background factors nor reading habits were related to phonological-processing skills.

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• In memoriam

  2015. Åke Hellström. Fechner Day 2015, xi-xii

  Conference

  Our very distinguished member, Professor Hannes Eisler, Stockholm University, has left us. He died on May 28, 2015, at the age of 91. He was a member of the ISP from its beginnings. At Fechner Day 2014 in Lund, Sweden, Hannes lectured on "Some research tips from 55 years' psychophysics." Informally, he named this presentation his "swan song."

  Hannes was born in Vienna, Austria, 1923, and at the age of 15 fled to Sweden to escape the Nazis. Initially Hannes worked as a farm hand but quickly progressed to study at high school and later at Stockholm University, where he became an adept of Gösta Ekman, the Swedish pioneer of quantitative psychology. After spending a year in S. S. Stevens’ lab at Harvard, Hannes was awarded his Ph.D. in Stockholm 1963. In 1994, as the result of a petition from all Swedish psychology professors, the Swedish government awarded Hannes Eisler the rank and honor of Professor – a rare recognition of scientific merit.

  During his long career, Hannes authored a large number of publications and made many important contributions to our field. His doctoral dissertation was about the relation between magnitude and category scales. Later on, he turned much of his interest toward time perception in people as well as in mice. Perhaps the most impressive of his contributions is the Parallel Clock model for temporal reproduction and comparison1, which arose from Hannes’ arduous and meticulous investigation of long known anomalies in time perception; specifically, breaks in psychophysical functions. Noting the positions of those breaks in reproduction data led him to the counter-intuitive realization that participants use a seemingly odd strategy in immediate reproduction of temporal intervals: subjectively matching the reproduction, not to the standard, but to one-half of the total duration. Using this model it is possible to estimate the psycho-physical function for time from reproduction data, and Hannes published a huge collection of temporal power function exponents2 – much cited but all too often with no understanding of how they were determined.

  Hannes was intellectually perspicacious and possessed research talent in abundance. Modesty, good nature, along with deep and diverse cultural interests, sense of humor, and appreciation of the good things in life, were some of his other characteristics. Scientific seminars on various topics were enriched by his insightful comments until a heart attack sadly ended his long life.

  I miss Hannes immensely, as a very good old friend, a respected senior colleague, and a mentor – even the word guru feels very appropriate.

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• Integration of stimulus dimensions in judgments of area and shape

  2015. Åke Hellström. Fechner Day 2015, 17-17

  Conference

  In the horizontal-vertical (H-V) illusion (Künnapas, 1958) the judged V/H ratio is larger than the physical ratio. This tendency is not found in V/H ratio judgments of rectangles (Gärling & Dalkvist, 1977), but these judgments are not based on the simple ratio of V and H: Level-curves (iso-judgment contours) of logarithmized data show that the larger dimension is more important than the smaller. Developmentally, judgments of rectangular area have been described as changing from adding V and H in children to multiplying  them in adults (Wilkening, 1979). However, level curves demonstrate deviations from simple models at all ages. Adults’ area judgments show a greater importance of the larger dimension, and also a greater importance of H than of V, but accurate modeling is difficult. Here, level-curve plots (using R’s contour function) prove invaluable for graphic guidance of modeling by displaying systematic judgment tendencies that go unnoticed with conventional factorial plots.

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• Time-order errors and standard-position effects in duration discrimination

  2015. Åke Hellström, Thomas H. Rammsayer. Attention, Perception & Psychophysics 77 (7), 2409-2423

  Article

  Studies have shown that the discriminability of successive time intervals depends on the presentation order of the standard (St) and the comparison (Co) stimuli. Also, this order affects the point of subjective equality. The first effect is here called the standard-position effect (SPE); the latter is known as the time-order error. In the present study, we investigated how these two effects vary across interval types and standard durations, using Hellstrom's sensation-weighting model to describe the results and relate them to stimulus comparison mechanisms. In Experiment 1, four modes of interval presentation were used, factorially combining interval type (filled, empty) and sensory modality (auditory, visual). For each mode, two presentation orders (St-Co, Co-St) and two standard durations (100 ms, 1,000 ms) were used; half of the participants received correctness feedback, and half of them did not. The interstimulus interval was 900 ms. The SPEs were negative (i.e., a smaller difference limen for St-Co than for Co-St), except for the filled-auditory and empty-visual 100-ms standards, for which a positive effect was obtained. In Experiment 2, duration discrimination was investigated for filled auditory intervals with four standards between 100 and 1,000 ms, an interstimulus interval of 900 ms, and no feedback. Standard duration interacted with presentation order, here yielding SPEs that were negative for standards of 100 and 1,000 ms, but positive for 215 and 464 ms. Our findings indicate that the SPE can be positive as well as negative, depending on the interval type and standard duration, reflecting the relative weighting of the stimulus information, as is described by the sensation-weighting model.

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