Russell D. Hamer, Ph.D.
Affiliate Reseach Professor, Department of Psychology
Florida Atlantic University
Office: BS 120
Phone: (516) 543-2109
Dr. Hamer is an Affiliate Research Professor in the Psychology Department at Florida Atlantic University at Boca Raton. He has been active in the field of Visual Neuroscience research for nearly four decades, with an emphasis on the study of visual development of human infants and development of models of phototransduction in rod and cone photoreceptors.
Current Research Focus: Neuroscientific Bases of Musical Rhythm
The domains of language and music represent two of the most remarkable, unique abilities of the human species and they are closely interconnected, both functionally and at the neuroanatomical/neurophysiological level. Speech communication is highly dependent on the prosody (rhythmical structure) of language, both for conveying semantic information as well as emotional information. It is a classic, yet revealing observation that severe stutterers can sing songs without stuttering. Humans’ unique facility in these domains, and the universality of music/rhythm and language in its various forms across cultures, makes them supremely important to study. Perception of rhythm and melody are deeply emblematic of, and inspirational for, the larger scientific inquiry into human pattern perception, human creativity and the aesthetic experience.
The current research program investigates rhythm production and perception, using synchronization and syncopation and continuation paradigms to evaluate the temporal precision, variability, and adaptability of internal timing mechanisms. Highly skilled professional percussionists will generate polyrhythms (non-isochronous) in a naturalistic musical environment using their percussive skills and musical training while playing Afro-Cuban rhythms on various hand-drums and percussion instruments such as traditional clave sticks. The experimental setting is designed to evoke optimal, musically engaging performance from the participants under the expectation that this will evoke the strongest internal rhythmical responses (“In the pocket! In the groove!”).
By means of carefully designed behavioral tasks, we measure the limits of precision of internal timing mechanisms that permit musicians (and dancers) to synchronize accurately, and to maintain complex syncopation even with highly non-isochronous rhythms (like rumba clave, or son clave) with precision that can maintain perceptual musical integrity. The precision of the underlying neural control mechanisms must be very high given that even non-musicians can synchronize with a metronome reference to within +-10 milliseconds. The human auditory system is extremely sensitive to separations between acoustic events down to thousandths of a second, and thus our internal “clocks” must function with extremely high temporal precision in order to be able to support this kind of musical/rhythmic behavior.
Dr. Hamer’s interest in this topic derives from a long-abiding love of Afro-Cuban music, rhythms and dance. He has, in fact, taught Cuban Salsa dance for over 24 years.
Other Research Interests
Prior to the current project, his long career in Sensory-Perceptual neuroscience has spanned a diverse range of topics:
His Ph.D. at the Institute for Sensory Research at Syracuse University focused on vibrotactile psychophysics and modeling of mechanoreceptor channels in humans obtained. His dissertation work introduced a model to account for human vibration sensitivity that was tied to the underlying physiology of the mechanoreceptors in human skin. The model predicted his new finding of so-called negative masking, when a masking stimulus that itself was sub-threshold could nevertheless enhance the detectability of an incremental stimulus by as much as 15 decibels.
Behavioral Measures of Human Visual Development
Dr. Hamer next applied his expertise in psychophysical methods to behavioral measures of visual development of human infants, starting with an invaluable Postdoctoral Fellowship with Prof. Davida Y. Teller in the Psychology Department at the University of Washington, Seattle, WA. There he focused on development of color vision over the first postnatal months, and on the development of scotopic (night) vision and spatial integration. His work was among the first objective demonstrations of color vision in infants as young as 4 weeks of age.
Electrophysiological Measures of Human Visual Development
Over the next decade and a half, Dr. Hamer continued research on visual development, but now utilizing the efficient and sensitive methods of steady-state electrophysiology (brain wave measures of visual responses using the visual evoked potential, VEP). This work was done in the laboratory of Dr. Anthony M. Norcia at the Smith-Kettlewell Eye Research Institute in San Francisco, CA. The research examined development of monocular and binocular grating acuity, contrast sensitivity and motion sensitivity.
In addition, Norcia, Hamer and colleagues showed that infants who had experienced interruption of normal binocular development (due to strabismus, for example) maintained strong monocular motion asymmetries in their steady-state motion-evoked responses even into adulthood. The nature of the asymmetry was a substantial difference in mVEP amplitude when periodically oscillating vertical sinewave gratings moved leftward vs when they moved rightward. In contrast, normal infants’ (monoc) motion VEPs mature quickly over the first 1-2 years and become symmetrical. The research thus introduced a monocular index of binocular maturation that was adopted in a number of other labs.
Adult Spatiotemporal Vision
In parallel with this work, Dr. Hamer worked with Dr. Christopher W. Tyler on adult spatiotemporal vision, analyzing human sensitivity to flicker as a function of light level. We were able to show flicker detection at very high frequencies (up to 100 Hz) in the periphery of vision, and showed that the peripheral visual field was substantially faster than the fovea, which had a maximum flicker frequency of only 50 Hz. In addition, we established optimal stimulus parameters to use in measures of temporal processing that took into account retinal inhomogeneities of temporal sensitivity.
Dr. Hamer investigated the detail of phototransduction, how rods and cones convert light energy into a bio-electric signal. He received funding for this project from the National Eye Institute of NIH. With colleagues from New York University, University of Pennsylvania, Australian National University and Smith-Kettlewell, he developed a computational model of phototransduction that accounted for a wide range of physiological data.
Measures of Abnormal Vision in Infants and Adults
He left Smith-Kettlewell in 2006 (maintaining an Affiliate status to the present day) and joined a lab in the Instituto de Psicologia at the Universidade de Sao Paulo (USP), in Sao Paulo, Brasil where he was a Visiting Professor teaching graduate students Sensation & Perception, Retinal Physiology and Phototransduction and Visual Development. His developmental research at USP overlapped his work at Smith-Kettlewell in that he continued with studies of visual development using the steady-state VEP approach. The work focused on examining infants born small for gestational age who had experienced inadequate nutrition during gestation. In this project, one graduate student received her Ph.D. under Dr. Hamer.
Also, during his tenure at USP, in collaboration with Profa. Mirella Gualtieri and colleagues, Dr. Hamer also studied psychophysical contrast processing in adults who were carriers of a devastating retinal disease, Leber’s Hereditary Optic Neuropathy, and in patients with Type 2 diabetes.
VEP Measures of Vernier and Contrast Processing Channels in Adults
Projects at USP also included studying Vernier processing in normal adults using the VEP as a function of contrast and spatial frequency. Two graduate students received advanced degrees (one Master's one Ph.D.) under Dr. Hamer while working on these projects.
In collaboration with scientists from the Universidade Federal do Para in Belem, Brasil, Dr. Hamer developed an approach to reveal contrast processing channels from VEP data.
While in Brasil. Dr. Hamer was invited to be an editor on the boards of Psychology & Neuroscience and Psicologia USP.
Hamer RD (2016). The visual world of infants. American Scientist 104: 96-101. PDF.
Hamer RD, Carvalho, FA & Ventura DF. (2013). Effect of contrast and gaps on sweep VEP measurement of human cortical vernier responses. Psychology & Neuroscience.6(2): 199-212. PDF
Gualtieri M, Bandeira M, Hamer RD, Damico FM, Moura ALA, Ventura DF. (2011) Contrast sensitivity mediated by inferred magno- and parvocellular pathways in type 2 diabetics with and without non-proliferative retinopathy. Invest Ophthalmol. Vis Sci. 52: 1151-1155. PubMed. IOVSsite.
Hamer, RD & Norcia, AM (2009) The Jitter Spatial Frequency Sweep VEP: a new paradigm to study spatiotemporal development of pattern- and motion-processing mechanisms in human infants. Psychology & Neuroscience 2: 163-177. PDF
Hamer, RD, Nicholas, SC, Tranchina, D, Lamb, TD & Jarvinen, JLP. (2005) Towards a unified model of vertebrate rod phototransduction. Visual Neuroscience, 22: 417-436. PubMed. PDF.
Hamer, R.D., Nicholas, S.C., Tranchina, D., Liebman, P.A. & Lamb, T.D. (2003). Multiple steps of phosphorylation of activated rhodopsin can account for the reproducibility of vertebrate rod single-photon responses. Journal of General Physiology, 122: 377-402. PDF
Hamer, R.D. (2000b). Analysis of Ca++-dependent gain changes in PDE-activation in vertebrate rod phototransduction . Molecular Vision 6, 265-286. PDF
Hamer RD, Norcia AM (1994) The development of motion sensitivity during the first year of life. Vis. Res. 34, 2387-2402. PubMed.
Hamer, R.D. and Mayer, D.L. (1994) The development of spatial vision. In: Principles and Practice of Ophthalmology, Chapter 42, Albert DM, Jakobiec FA (Eds.), W.B. Saunders Co., Philadelphia, PA., pp. 578-608.
Hamer RD, Tyler CW (1992) Analysis of visual modulation sensitivity. V. Faster visual response for G- than for R-Cone pathway? J. Opt. Soc. Am.A , 9, 1889-1904. PDF.
Norcia AM, Tyler CW, Hamer RD. (1990) Development of contrast sensitivity in the human infant. Vision Res.; 30(10): 1475-86. PDF.
Hamer RD, Verrillo RT, Zwislocki JJ. (1983) Vibrotacile masking of Pacinian and non-Pacinian channels. J Acoust Soc Am.; 73(4): 1293-303. JASA.
Hamer RD, Alexander KR, Teller DY. (1982) Rayleigh discriminations in young human infants. Vision Res.; 22(5): 575-577. VisionResearch.