Picture this; You and a friend decide to go to the movies, but you are late getting to the cinema. As you walk into the dark theatre, you are scanning the room for a place to sit. The next day at work, your co-worker tells you they waved at you in the theatre but you didn’t wave back. How did you miss that when it was right in front of you? Not taking notice to an event that has taken place in the obvious is a phenomenon called “inattentional blindness”. Many scientific studies have investigated different variables that can affect how people attend to events, however studies investigating the neurophysiological activity during these events is limited. Luckily, Attention and Capacity Limits in Perception: A Cellular Metabolism Account by Bruckmaier, Tachtsidis, Phan, and Lavie (2020) provides readers with insight about the cellular activity in the visual cortex of the human brain during perceptual processing.
The main focus of this study was to investigate the effects that limited cellular metabolism has on perceptual processing demands. There is a well-known idea that cerebral energy supply sets a tough limit on mental processing. This means that the energy required for mental processes is not unlimited, and therefore if we are lacking the sufficient amount needed for a mental activity, our perception suffers. To examine the cellular energy activity in the visual cortex of the human brain, the level of cytochrome c oxidase (oxCCO) was measured by a broadband near-infrared spectroscopy (BNIRS). The mitochondrial enzyme, oxCCO, was used to indicate the cellular oxidative metabolism during the attention tasks and with the different perceptual loads.
Two experiments were conducted. In the first experiment it was investigated whether the metabolism levels linked with unattended processing could be modulated by perceptual load. A perceptual load manipulation was presented to participants, along with a task-irrelevant stimulus. A series of crosses, varying in color and orientation, were rapidly displayed on a black background with a flickering checkerboard in the periphery region of the screen. Participants were told to ignore the checkerboard and detect the instructed target stimuli they were given beforehand. There was a low-load condition where targets were given based solely on color, whereas in the high-load condition, targets were determined by color and orientation. The BNIRS was used to measure the signal of oxCCO from other chromophores by using the full light spectrum range of 780 – 900 nm, where the general peak of oxCCO is 830 nm. The data collected was based off of the oxCCO mean signals in each condition.
In the second experiment the influence of perceptual load on cellular metabolism levels in attended and unattended processing were compared. In this experiment the task stimuli were altered in order to reveal better BNIRS signals in each stimulus. The size of the crosses was increased and a white swirl pattern was placed over the crosses. These modifications produced greater oxCCO signal strength and increased the activation of the striate and extrastriate visual cortex areas.
The results of the first experiment indicated that the mean oxCCO response was greater when the distractor stimulus was present versus absent in the attention task. Additionally, the oxCCO signal paired to the presence of the distractor stimulus was reduced in the high-load condition compared to the low-load. These findings were consistent with the second experiment. Furthermore, in the second experiment, to investigate the impact of perceptual load on attended processing, the effect of load on the oxCCO signals in the target-only attended task conditions was analyzed. The results show that the oxCCO response to the target-only conditions were higher in the high-load. Finally, the results suggested a trade-off effect that demonstrates how cerebral metabolism levels are flexible for mental processing loads while emphasizing the importance of attention for control in metabolic source allocation.
These findings show the influence of cellular metabolism limits on perceptual capacity and attention, along with changes in the load levels of tasks. So, the next time you exhibit inattentional blindness, perhaps you will consider neurophysiological aspects of your perception.
Bruckmaier, M., Tachtsidis, I., Phan, P., & Lavie, N. (2020). Attention and Capacity Limits in Perception: A Cellular Metabolism Account. The Journal of Neuroscience, 40(35), 6801-6811.
