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Vision Research 47 (2007) v–vii

In Memoriam

Henk Spekreijse (1940–2006)

Henk Spekreijse suffered a fatal heart attack in Amster-dam on 20 October 2006. From 1991 to 2004 Henk waschairman of the board and editor in chief of Vision Re-

search. Under his guidance the journal flourished andexpanded to 28 issues per year. He worked with Elsevierto introduce and fund the pre-ARVO special symposiaand initiated the publication of special issues of the journal,which bring together scientists from different disciplines todiscuss questions of high interest in vision research.

In parallel with his life in research he played a majoradministrative role in the international development of vi-sion research. Within Europe, he was instrumental inestablishing the Netherlands Ophthalmic Research Insti-tute as the focus of collaboration between sixteen ophthal-mology departments in The Netherlands and Belgium, andserved as director of research at that Institute.

Spekreijse has long been recognised as one of theoutstanding visual researchers of his time. His was a largelaboratory, scientific home over the years for many post-doctoral fellows and over fifty Ph.D. students. A remark-able number became well-known scientists with their ownlaboratories. In 1985 he was elected Fellow of the Nether-

0042-6989/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.doi:10.1016/j.visres.2007.01.004

lands Royal Academy of Arts and Science. In 2003 a Fest-schrift organized by his ex-students was unexpectedlyinterrupted by the entrance of a representative of theQueen who inducted an astonished Henk Spekreijse asKnight in the Order of Lion of The Netherlands.

After receiving his master’s degree in experimental phys-ics from Delft University, Spekreijse carried out his Ph.D.research under the inspiring supervision of late and muchmissed Henk van der Tweel. At that time the DutchPh.D. examination was an ordeal. Dressed in formal blacktie and flanked by two supporters also in formal black tie,Spekreijse stood in a 17th-century church before severalhundred attendees, including black-gowned professorsfrom many Dutch universities. As an extra twist the Dutchsystem required the candidate to add to the thesis a list ofseveral nontrivial ‘‘propositions’’ that had no relation tothe thesis topic. The outstanding scientific merit of the the-sis research having soon been established to everyone’s sat-isfaction, professorial friends of van der Tweel relaxed bygrilling Spekreijse on his propositions, including one onthe strange mechanical properties of tomato ketchup anda second on what might be revealed by cleaning one of

vi In Memoriam / Vision Research 47 (2007) v–vii

Rembrandt’s most famous works; the edge to this grillingwas that the supervisor was expected to resign his chair ifhis student failed the examination.

The wide distribution of over one thousand copies of Spe-kreijse’s thesis, published as a book in 1966, immediatelyestablished him as a pioneer in the application of nonlinearsystems analysis to electrophysiology and attracted theattention of several influential scientists: doors were opened.The importance of nonlinear analysis has been expressed byReichardt and Poggio (1981) as follows: ‘‘every nontrivialcomputation has to be essentially nonlinear, that is not rep-resentable (even approximately) by linear operations’’.

Spekreijse spent 1967–1968 at the Naval Medical Re-search Institute in Bethesda, Maryland, where he learntfrom H. Wagner and M. Wolbarscht the technique ofrecording single unit activity from the isolated fish retinaand collaborated on several published studies on the colourcoding of the intra-retinal action potential and (with Nor-ton) on the colour coding and receptive field organizationand dynamics of the retinal S-potential.

On his return to The Netherlands Spekreijse’s progresswithin the distinguished and highly competitive biomedicalcommunity was rapid: from Ph.D. in 1966 to reader in1971 and in 1977 appointed full professor of visual systemsanalysis in the Laboratory of Medical Physics at the Uni-versity of Amsterdam.

In 1965 Spekreijse and van der Tweel had reported that,in humans, monocular stimulation with sinusoidally mod-ulated light of frequency F Hz produced an electricallyevoked response, recordable from scalp electrodes, andthat the response was an almost pure sinusoid of frequency2F Hz combined with a small F Hz component. By defini-tion, the 2F component was produced by a nonlinearity.The addition of sufficient noise (an ‘‘auxiliary signal’’) tothe monocular sinusoidal flicker abolished the 2F Hz re-sponse component, sparing the F Hz component so thatthe visual system behaved approximately linearly (the line-arizing phenomenon). In his Ph.D. thesis, Spekreijse de-scribed the nonlinearity as an asymmetric rectifier. Thisproved to be an innovative concept: rectifiers feature inmodels of the visual and auditory pathways proposed bymany laboratories over the following forty years. By usinga sinusoid as the auxiliary signal in his thesis work, heintroduced a two-sinewave approach to nonlinear systemsanalysis and was able to analyze the human visual systeminto two parallel pathways, each consisting of a sequenceof linear and nonlinear stages. In subsequent work on gold-fish retina and monkey LGN, Spekreijse and colleaguesidentified the rectifier-like characteristic with the behaviourof ganglion cells.

From his return to The Netherlands in 1968 until hisretirement, Spekreijse continued to be active in researchon visually evoked electric (and later magnetic) responsesof the human brain, collaborating with Estevez, Dangelie,Regan, van den Berg, van der Tweel and van Dijk on awide range of studies including interocular suppression,brain responses to luminance and chromatic contrast, ste-

reoscopic depth, the onset and offset of motion, colour vi-sion, colour blindness, texture segregation and audio-visualinteraction. With Munck, Maire and van Dijk he publishedsophisticated mathematical approaches to the source loca-tion of evoked electrical and magnetic brain responses.

Building on his experience in the Bethesda laboratory,Spekreijse established in Amsterdam a laboratory for reti-nal research that was soon noted internationally for itscombination of productivity, high level of scientific insightand technical skill. There he collaborated with colleagues,including van den Berg, van Norren, Schellart, van Dijkand Kamermans. In single-unit studies of goldfish retinaand on monkey LGN they introduced to single-unit elec-trophysiology the concept that for strongly modulatedflicker stimulation the addition of an auxiliary signal cancause the essentially nonlinear stage expressed at ganglioncell level to mimic linear behaviour and found that evenneural noise can produce this linearizing phenomenon fornear-threshold stimuli. This concept is important, not onlyfor a deeper understanding of information processing atcellular level but also in general for the interpretation ofpsychophysical data in humans. Spekreijse and colleaguesdeveloped a realistic model for the feed forward/feedbackpathways between cones and horizontal cells in goldfishretina, showed that this organization provides a physiolog-ical basis for the perceptual phenomenon of colour con-stancy, and found that the phenomenon is establishedalready at the level of the cone pedicle.

During the last few years Spekreijse and colleaguesLamme, Super, Roelfsema, Khayat, Landman, Scholte,van der Togt and Witteveen published in the highest-im-pact journals a remarkable number of papers on highervisual processes in primates. By combining electrophysiol-ogy with psychophysics in alert behaving monkeys theymade the important discovery that object-based attentionexpresses itself by increased neural firing at the level ofthe striate cortex. They showed how the synchrony of firingin V1 neurons relates to visual detection and contourgrouping, and discovered neural correlates of the visualstability of the perceived world across saccades. By record-ing the magnetic field of the human brain (MEG) theyfound a putative physiological basis for awareness, andby combining MEG with fMRI discovered neural corre-lates of scene segmentation.

Spekreijse himself wrote that his main research interests‘‘concern the introduction of findings from basic researchinto ophthalmological and neurological practice’’ and in-deed from the moment he became a professor of medicalphysics the formidable scientific expertise and technicalfacilities of the department were available to support andstrengthen clinical research carried out in the Faculty ofMedicine on patients with a wide variety of ophthalmolog-ical and neurological disorders. He was closely involved inclinical diagnosis, largely through his supervision of theElectrophysiology Laboratory of the Amsterdam Universi-ty Eye Clinic. He had a long-term interest in the develop-ment of non-invasive techniques for monitoring the visual

In Memoriam / Vision Research 47 (2007) v–vii vii

status of patients, especially of pre-verbal infants who arenotoriously difficult to test. To that end his researchgroup’s lengthy and laborious work on the developmentof visual evoked potentials from the age of a few weeksup to ten years provided physicians with a normal baselineof infant and child development. Without that baseline thetechnique would not have enjoyed its current level of clin-ical use. More recently Spekreijse worked to attract thelarge funding and technical support required to apply thenon-invasive brain imaging techniques of functional MRIand magneto-encephalography to the assessment of neo-nates and premature babies—truly an example of the mostadvanced technology and scientific skills being applied tothe benefit of ophthalmological and neurological patients.

Over the years, Spekreijse’s laboratory was host to manyvisiting scientists, only some of whom were already wellestablished. He helped to establish the reputation of manyyoung researchers whose home country provided only slimsupport for science. In addition to research experience, thegenerous after-work hospitality of Henk and his wife,Yvonne, was a practical realization of the internationaliza-tion of scientific research that has been appreciated bymany throughout the world.

Spekreijse played an important role in enhancing theinternational visibility of Dutch biomedical research, andto that end introduced innovations in research training.Within The Netherlands he was active in many administra-tive and planning issues concerned with scientific facilitiesand funding. He was forceful and determined in bringingabout changes that he considered to be for the future goodof neuroscience and biomedical research in The Nether-lands. But sadly, and to the dismay of his friends, somechanges were not achieved without lasting personal cost.Without the unfailing support of Yvonne Spekreijse–vander Heyden through difficult times it is unlikely that he

could have made the outstanding contributions to scienceand to his country for which he was widely respected andadmired.

Henk and Yvonne had two daughters, Stephanie andDieuwertje, who gave him many reasons for his quiet pridein them. During the last few years he and Yvonne took de-light in their new roles as grandparents.

‘‘What is most impressive about Henk’s work apartfrom its consistent high quality is its breadth. He has madecontributions at the highest level to retinal biophysics, hu-man psychophysics, infant development studies, mathe-matical modeling, electric and magnetic evokedpotentials, and single-unit recording in the visual pathwayof anaesthetized and awake behaving animals’’ (ColinBlakemore). ‘‘. . . in 1969 I heard Dr. Spekreijse talk abouthis new use of nonlinear analysis. Over the years I havebeen continually amazed by Spekreijse’s mathematicaland scientific genius applied to many diverse problems invision research. He is internationally recognised as one ofthe most outstanding vision scientists of his generation’’(Bob Shapley). ‘‘I do not know any other person whose sci-entific contributions follow so closely the idea of ARVO tobring together basic neuroscience of vision and clinicalophthalmology’’ (Heinz Waessle).

References

Spekreijse, H., & van der Tweel, L. H. (1965). Linearization of evokedresponses to sine wave modulated light by noise. Nature, 205, 913.

Reichardt, W., & Poggio, T. (Eds.). (1981). Theoretical approaches in

neurobiology. Cambridge, MA: MIP Press. MIP Press (p. 187).

David ReganCenter for Vision Research, Department of Psychology,

York University, North York, Ont., Canada M3J 1P3

E-mail address: dregan@yorku.ca