Selected publications:
Stephen L. Macknik (in press) Visual masking approaches to visual awareness. Progress in Brain Research.
Susana Martinez-Conde, Stephen L. Macknik, Xoana G. Troncoso & Thomas A. Dyar (2006) Microsaccades counteract visual fading. Neuron, 49, pp.297-305.
Stephen L. Macknik, Ph.D.
Director, Laboratory of Visual Perception
Divisions of Neurosurgery and Neurobiology
Peter U. Tse, Susana Martinez-Conde, Alexander A. Schlegel, Stephen L. Macknik (2005) Visibility and visual masking of simple targets are confined to areas in the occipital cortex beyond human V1/V2. Proceedings of the National Academy of Sciences (USA), 102(47), pp.17178-17183.
Xoana G. Troncoso, Stephen L. Macknik & Susana Martinez-Conde (2005) Novel visual illusions related to Vasarely's 'nested squares' show that corner salience varies with corner angle. Perception, 34(4), pp.409-420.
Stephen L. Macknik (2005) Modern Imaging Approaches in Neuroscientific Research. Barrow Quarterly, 21(3), pp.38-43.
Stephen L. Macknik & Susana Martinez-Conde (2004) Dichoptic visual masking reveals that early binocular neurons exhibit weak interocular suppression: implications for binocular vision and visual awareness. Journal of Cognitive Neuroscience, 16:6, pp. 1049-1059.
Stephen L. Macknik & Susana Martinez-Conde (2004) The spatial and temporal effects of lateral inhibitory networks and their relevance to the visibility of spatiotemporal edges. Neurocomputing, 58-60, pp.775-782.
Susana Martinez-Conde, Stephen L. Macknik & David H. Hubel (2004) The role of fixational eye movements in visual perception Nature Reviews Neuroscience, 5, pp. 229-240.
Martinez-Conde S, Macknik SL, & Hubel DH. (2002) The function of bursts of spikes during visual fixation in the awake primate lateral geniculate nucleus and primary visual cortex. Proceedings of the National Academy of Sciences (USA), 99(21), pp.13920-13925.
Macknik, SL & Martinez-Conde, S, & Haglund, MM (2000) The Role of Spatiotemporal Edges in Visibility and Visual Masking. Proceedings of the National Academy of Sciences (USA) Vol. 97(13), pp.7556-7560.
Martinez-Conde, S, Macknik, SL & Hubel, DH (2000) Microsaccadic Eye Movements and Firing of Single Cells in the Striate Cortex of Macaque Monkeys. Nature Neuroscience Vol. 3(3), pp. 251-258.
Macknik, SL & Haglund, MM (1999) Optical Images of Visible and Invisible Percepts in the Primary Visual Cortex of Primates Proceedings of the National Academy of Sciences (USA) Vol. 96(26) pp. 15208-15210.
Macknik, SL & Livingstone, MS (1998) Neuronal correlates of visibility and invisibility in the primate visual system. Nature Neuroscience Vol. 1(2) pp.144-149.
My
research is focused on the neural correlates of visibility. What is required
for an object to be visible? One might think, at first, that visibility
should require only that light falls on the retina. But it can be more
complicated, as shown in the illusions below:
Unfilled Flicker, the
Standing Wave of Invisibility, the
Dichoptic Standing Wave, and the
Stoper-Mansfield Effect. Illusions of invisibility such as these show that a
stimulus can be projected onto our retinas, and nevertheless be partly or
wholly invisible. By using these types of illusions one can
focus on the portions of the stimulus that generate neuronal responses best
correlated to visibility. Transient bursty activity occurs when a stimulus
turns either on or off (the stimulus’ temporal edges), or when the eyes
move. This same transient activity also occurs at the spatial edges of the
stimulus. Moreover, when this transient – as opposed to sustained – activity
is suppressed, visibility is decreased. We therefore conclude that
visibility is linked to the spatiotemporal edges of stimuli, and that the
neural correlate of spatiotemporal edges is transient bursty activity.
To do: Press the button above to vary the duration and size of the box.
To notice: When the box flickers slowly, each flicker is of long duration and the box appears to be filled-in. When it flickers quickly (short duration flicker) it appears to be "unfilled": the center appears to be about the same color as the background. But even in the unfilled condition, the inside of the box is filled from the edges to some small extent, which is why we see a black frame. When the box flickers quickly and is skinny, however, the edges of the box are closer together and it appears filled-in, even though it has short duration flicker.
Unfilled Flicker is an illusion in which we can see that it is the edges of stimuli that evoke the strongest neural signals in our brains.
SOURCE:
Macknik, SL & Martinez-Conde, S, & Haglund, MM (2000) The Role of Spatiotemporal Edges in Visibility and Visual Masking. Proceedings of the National Academy of Sciences (USA) Vol. 97(13) pp. 7556-7560.
The Standing Wave of Invisibility
To do: Use the arrow buttons above the illusion to vary the distance of the masks (outer two bars) from the target (the central bar). Left arrow to move masks in, right to move masks out. This will vary the effect of the masks on the target: the closer the masks the more powerful the effect on the target. Pressing and holding the arrow buttons gives the best results.
To notice: As the distance between the mask and the target decreases, so does the visibility of the target.
The Standing Wave of Invisibility is an illusion in which the visibility of the central bar in the display above (the target) is decreased by flanking bars (the mask), which flicker in alternation with the target. The illusion shows that a set of masks can render a target perpetually invisible, even though the masks don’t overlap the target in either position or timing.
SOURCES:
Macknik, SL & Martinez-Conde, S, & Haglund, MM (2000) The Role of Spatiotemporal Edges in Visibility and Visual Masking. Proceedings of the National Academy of Sciences (USA) Vol. 97(13) pp. 7556-7560.
To do: Wear 3D-glasses that have one red lens and one blue or green lens. Then operate the controls as in the Standing Wave of Invisibility. To get a free pair of 3D anaglyph glasses in the mail, go to Rainbow Symphony's website. Use the arrow buttons above the illusion to vary the distance of the masks (outer two bars) from the target (the central bar). Left arrow to move masks in, right to move masks out. This will vary the effect of the masks on the target: the closer the masks the more powerful the effect on the target. Pressing and holding the arrow buttons gives the best results.
To notice: As the distance between the mask and the target decreases, so does the visibility of the target.
The Dichoptic Standing Wave is similar to The Standing Wave of Invisibility in that it is an illusion in which the visibility of the central bar in the display above (the target) is decreased by flanking bars (the mask), which flicker in alternation with the target. The illusion shows that a set of masks can render a target perpetually invisible, even though the masks and target are in separate eyes.
To do: Press the button above to turn on a circular mask within the box. Press it again to turn the mask off.
To notice: With the mask on, the black box is inhibited from completely filling-in (notice the white aura around the circular mask). Without the mask, the box appears fully filled-in.
The Stoper-Mansfield Effect is an illusion in which we can visualize inhibitory activity within our own brains.
SOURCES:
Macknik, SL & Martinez-Conde, S, & Haglund, MM (2000) The Role of Spatiotemporal Edges in Visibility and Visual Masking. Proceedings of the National Academy of Sciences (USA) Vol. 97(13) pp. 7556-7560.
Paradiso, MA & Nakayama, K (1991) Brightness perception and filling-in Vision Research Vol. 31 pp.1221-1236.
Stoper, AE & Mansfield, JG (1978) Metacontrast and paracontrast suppression of a contourless area Vision Research Vol. 18 pp.1669-1674.
Contact Me:
Stephen L. Macknik
Barrow Neurological Institute
350 W. Thomas Rd.
Phoenix, AZ 85013
USA
Phone: +1 (602) 406-8091
FAX: +1 (602) 406-4172