Pupil dilation reflects perceptual selection and predicts subsequent stability in perceptual rivalry

Wolfgang Einhäuser, James Stout, Christof Koch, Olivia Carter
PNAS | February 5, 2008 | vol. 105 | no. 5 | 1704-1709

During sustained viewing of an ambiguous stimulus, an individual's perceptual experience will generally switch between the different possible alternatives rather than stay fixed on one interpretation (perceptual rivalry). Here, we measured pupil diameter while subjects viewed different ambiguous visual and auditory stimuli. For all stimuli tested, pupil diameter increased just before the reported perceptual switch and the relative amount of dilation before this switch was a significant predictor of the subsequent duration of perceptual stability. These results could not be explained by blink or eye-movement effects, the motor response or stimulus driven changes in retinal input. Because pupil dilation reflects levels of norepinephrine (NE) released from the locus coeruleus (LC), we interpret these results as suggestive that the LC–NE complex may play the same role in perceptual selection as in behavioral decision making.

Fulltext: http://www.pnas.org/cgi/reprint/105/5/1704

A Fast, Reciprocal Pathway between the Lateral Geniculate Nucleus and Visual Cortex in the Macaque Monkey

Farran Briggs and W. Martin Usrey
The Journal of Neuroscience, May 16, 2007, 27(20):5431-5436;

Neurons in the lateral geniculate nucleus (LGN) not only provide feedforward input to primary visual cortex (V1), but also receive robust feedback from the cortex. Accordingly, visual processing in the LGN is continuously influenced by previous patterns of activity. This study examines the temporal properties of feedforward and feedback pathways between the LGN and V1 in the macaque monkey to provide a lower bound on how quickly the cortex can influence the LGN. In so doing, we identified a subclass of corticogeniculate neurons that receives direct, suprathreshold input from the LGN that is similar in latency to that directed to other recipient neurons (4.2 ± 0.4 vs 4.0 ± 0.2 ms). These neurons also provide feedback to the LGN that is significantly shorter in latency than that supplied by corticogeniculate neurons lacking LGN input (5.1 ± 1.3 vs 11.1 ± 2.3 ms, respectively). Across our sample of corticogeniculate neurons, the shortest combined visual response latency and feedback latency was 37 ms (mean, 52.5 ± 3.8 ms), indicating that visual signals can rapidly travel from the periphery to the cortex and back to the LGN.

Fulltext: http://www.jneurosci.org/cgi/reprint/27/20/5431

Effects of Long-Term Object Familiarity on Event-Related Potentials in the Monkey

Jessie J. Peissig, Jedediah Singer, Keisuke Kawasaki, David L. Sheinberg
Cerebral Cortex June 2007;17:1323--1334 doi:10.1093/cercor/bhl043

Although some change in the neural representation of an object
must occur as it becomes familiar, the nature of this change is not
fully understood. In humans, it has been shown that the N170—an
evoked visual potential—is enhanced for classes of objects for
which people have visual expertise. In this study, we explored
whether monkeys show a similar modulation in event-related
potential (ERP) amplitude as a result of long-term familiarity by
recording ERPs with chronically implanted electrodes over extended
training periods spanning many sessions. In each of 3
experiments, we found larger amplitude visual evoked responses to
highly familiar images for the time period of 120--250 ms after
stimulus onset. This difference was found when the monkeys were
trained in an individual-level discrimination task, in a task that
required only color discrimination, and even following a viewingonly
task. We thus observed this familiarity effect across several
tasks and different object categories and further found that the
difference between ‘‘familiar’’ and ‘‘novel’’ became smaller as the
animals gained experience with the previously unfamiliar objects
across multiple test sessions. These data suggest that changes in
visual responses associated with familiarity are evident early in the
evoked visual response, are robust, and may be automatic, driven at
least in part by repeated object exposure.

Activity of Inferior Temporal Cortical Neurons Predicts Recognition Choice Behavior and Recognition Time during Visual Search

Ryan E. B. Mruczek and David L. Sheinberg
The Journal of Neuroscience, March 14, 2007, 27(11):2825-2836; doi:10.1523/JNEUROSCI.4102-06.2007

Although the selectivity for complex stimuli exhibited by neurons in inferior temporal cortex is often taken as evidence of their role in visual perception, few studies have directly tested this hypothesis. Here, we sought to create a relatively natural task with few behavioral constraints to test whether activity in inferior temporal cortex neurons predicts whether or not a monkey will recognize and respond to a complex visual object. Monkeys were trained to freely view an array of images and report the presence of one of many possible target images previously associated with a hand response. On certain trials, the identity of the target was swapped during the monkeys' targeting saccade. Furthermore, the response association of the preswap target and the postswap target differed (e.g., right-to-left target swap). Neural activity in cells selective for the preswap target was significantly higher when the monkeys' response matched the hand association of the preswap target. Furthermore, the monkeys' response time was predicted by the magnitude of the presaccadic firing rate on nonswap trials. Our results provide additional support for the role of inferior temporal cortex in object recognition during natural behavior.

Fulltext: http://www.jneurosci.org/cgi/reprint/27/11/2825

The Effect of Spatial Attention on Contrast Response Functions in Human Visual Cortex

Giedrius T. Buracas and Geoffrey M. Boynton

Previous electrophysiology data suggests that the modulation of neuronal firing by spatial attention depends on stimulus contrast, which
has been described using either a multiplicative gain or a contrast-gain model. Herewemeasured the effect of spatial attention on contrast
responses in humans using functional MRI. To our surprise, we found that the modulation of blood oxygenation level-dependent (BOLD)
responses by spatial attention does not greatly depend on stimulus contrast in visual cortical areas tested [V1, V2, V3, andMT
(middle
temporal area)]. An additive model, rather than a multiplicative or contrast-gain model best describes the attentional modulations in V1.
This inconsistency with previous single-unit electrophysiological data has implications for the population-based neuronal source of the
BOLD signal.