What Fascinates Me About Sensory-Perceptual Neuroscience
How do we see? Feel, smell, hear, taste? How do humans make art, music, keep incredibly precise musical timing? How do we come to know what we know, starting from our neonatal state when our journey into the vast world of sensations and perceptions blossoms. From sensation to perception to cognition/emotion and action, the range of experience and flexibility and creativity of humans amazes and fascinates me.
Current Research Focus
After many years of basic research into the elements of sensation and visual perception derived from single-cell physiology, psychophysics and modeling (elaborated below), my current research has turned to analysis of art and what lessons it can provide about perception: how does the visual system come to “understand” scenes? And in the case of pictorial art, the visual brain has some daunting challenges to overcome in order to understand, perceive the various elements of a painting and organize them into a coherent 3D scene. From the artist’s imagination, to daubs of paint on a 2D canvas, artists know how to evoke a robust 3D perception in our brain. Semir Zeki wrote: “...visual art obeys the laws of the visual brain and thus reveals these laws to us.” (Zeki, 1999, 2001). The “rub” is: what “laws” and how does art reveal them?
Humans have been making pictorial art for at least 50,000 years. Thus, many neuroscientists today view art as a bona fide science, a study of the devices and pictorial gestures that can successfully convey robust 3D scenes fecund with color, implied movement, often rich with human emotion and universal symbolic content.
Specifically, I have been doing a deep-dive into the art of the Belgian Surrealist, René Magritte (1898-1967). Rene Magritte once said “...the function of art is to make poetry visible, to render thought visible”. His poetry emerged on the canvases by meticulous, aesthetically engaging depiction of objects and scenes replete with surprise, contradiction, and what Magritte called “poetic shock”: the juxtaposition of related objects in utterly unexpected contexts. He was, and thought of himself as, a philosopher more than an artist – he did not even enjoy painting. . He once said: “...the function of painting is to make poetry visible, to render thought visible”.
Magritte had a sophisticated understanding of perception as representation in the brain. His works often deliberately “messed with” our visual brain’s expectations, to surreal effect. In one famous series of works spanning decades of his career, Magritte explored perceptual paradoxes by painting objects that appear to reveal what they conceal (7 versions of “La Condition Humaine” between 1931 and 1949, and 3 versions of “La Belle Captive” between 1931 and 1948). Glance once and an object is seen as figure; glance again and it is background. The works are replete with visual paradoxes induced by Magritte’s clever, intuitive manipulation of our visual system’s “rules” that, under normal (real) circumstances, permit a seamless, automatic identification of, segregation of, and organization of objects into a robust 3D scene. And he then delights in violating our brain’s “expectation”, thereby revealing to ourselves, our own visual system’s “rules” by their violation, creating what Magritte called “poetic shock”.
So far I have published three papers that analyze two of Magritte’s famous works (see my CV). In 2023, I was invited to give a lecture on Magritte at the Norton Museum of Art in West Palm Beach, FL. The lecture can be viewed on The Norton Channel on YouTube: (https://youtu.be/UhJDpX4zQRU?si=masmVDwtnVXPqYGr ).
Where I come from: my past scientific journey
Vibrotactile Masking and Sensitivity
My research in neuroscience has been quite eclectic. In my graduate work, I studied vibration sensitivity in the skin (amazing factoid: under some conditions, I found that we can detect vibrations as small as 0.05 microns, about 150 times smaller than the diameter of a human red blood cell).
Visual Development of Human Infants
For 20 years, I studied visual development of infants, normal development of acuity, contrast sensitivity, color vision, motion sensitivity. This work was done in collaboration with creative and brilliant colleagues: Davida Y. Teller (University of Washington, Seattle, WA); Anthony M. Norcia, Christopher W. Tyler and Arthur Jampolsky at the Smith-Kettlewell Eye Research Institute (San Francisco, CA); Dora Fix Ventura and Valtenice de Cássia Rodrigues de Matos Françaat the Departamento de Psicologia, Universidade de São Paulo, São Paulo, Brazil. (among others: see my CV and my personal website).
Spatio-Temporal Processing in Human Vision
Christopher W. Tyler did a series pf psychophysical experiments and modeling of flicker sensitivity. Specifically, we examined human’s ability to detect rapidly flickering stimuli (as distinguishable from steady lights) across the retina as a function of retinal illuminance. In general, if the stimuli are carefully chosen to as to (i) not adapt the visual system to flicker, (ii) test patches of retina having homogeneous temporal-processing properties, (iii) prevent detection of flicker by rods at low retinal illuminances, we found that critical flicker frequency (CFF), the fastest flicker that could be reliably distinguished from a steady light, increased linearly over 5 to 6 log units of retinal illuminance (Ferry-Porter Law). We showed that the central fovea was much slower (55 Hz max CFF) than the periphery (>100Hz 35 deg in peripheral retina). Moreover, Hamer &Tyler (1992) showed that the slope of the Ferry-Porter function was significantly steeper when a green light was flickered than when a red light was used. The steeper slope implies faster temporal processing. (see CV).
Phototransduction Modeling: How Photoreceptors Convert Light Energy Into a Bioelectric Signal
Another major branch of my research was devoted to understanding and modeling how photoreceptors (rods and cones) convert light energy into an electrical signal (phototransduction) that initiates the flow of neural signals to the brain. This research tackled a 25-year-old conundrum in the field: namely how rods are able to reliably signal the capture of single photons of light despite the inherently aleatory biochemical reactions that photon-capture elicits. We developed a model that was able to account for single-photon response statistics as well as responses to intense light drives the rods into a highly light-adapted, nonlinear state. My colleagues in this project were: Daniel Tranchina (Courant Institute of Mathematics and Department of Biology, NYU, NY, NY), Trevor Lamb (Australian National University, Canberra, Australia ), Paul A. Liebman (Univrsity of Pennsylvania Perelman School of Medicine, Philadelphia, Pennsylvania) and Spero C. Nicholas (Smith-Kettlewell Eye Research Institute, San Francisco, CA).
My foray into this topic was initially sparked by a motivation to improve on some features of, and avoid the limitations of, prominent models of cone phototransduction in primates and humans. Christopher W. Tyler and I developed a model of primate and human cone phototransduction that captured many of the key quantitative features of the data while avoiding physiologically unrealistic implications of the current models at the time. (see CV for papers on phototransduction)