Profiles

Åke Hellström, porträtt. Foto: Niklas Björling.

Åke Hellström

Professor emeritus

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Arbetar vid Psykologiska institutionen
E-post hellst@psychology.su.se
Besöksadress Frescati hagväg 14
Postadress Psykologiska institutionen 106 91 Stockholm

Om mig

Main interests are in the field of perception and psychophysics with neuropsychological applications. Of particular concern are the processes that occur when two stimuli are compared, the reasons for the systematic errors that occur then, and applications of computerized tests, built thereon, in neuropsychological diagnostics. Other interests include time perception, speech perception, person perception, aesthetic perception, and the subjective color phenomena.

Publikationer

I urval från Stockholms universitets publikationsdatabas
  • 2015. Heidi Selenius, Åke Hellström. Psychiatry, Psychology and Law 22 (4), 586-598

    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.

  • Konferens In memoriam
    2015. Åke Hellström. Fechner Day 2015, xi-xii

    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.

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

    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.

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

    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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Senast uppdaterad: 16 maj 2017

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