Paradoxical relationship between speed and accuracy in olfactory figure-background segregation

Abstract

In natural settings, many stimuli impinge on our sensory organs simultaneously. Parsing these sensory stimuli into perceptual objects is a fundamental task faced by all sensory systems. Similar to other sensory modalities, increased odor backgrounds decrease the detectability of target odors by the olfactory system. The mechanisms by which background odors interfere with the detection and identification of target odors are unknown. Here we utilized the framework of the Drift Diffusion Model (DDM) to consider possible interference mechanisms in an odor detection task. We first considered pure effects of background odors on either signal or noise in the decision-making dynamics and showed that these produce different predictions about decision accuracy and speed. To test these predictions, we trained mice to detect target odors that are embedded in random background mixtures in a two-alternative choice task. In this task, the inter-trial interval was independent of behavioral reaction times to avoid motivating rapid responses. We found that increased backgrounds reduce mouse performance but paradoxically also decrease reaction times, suggesting that noise in the decision making process is increased by backgrounds. We further assessed the contributions of background effects on both noise and signal by fitting the DDM to the behavioral data. The models showed that background odors affect both the signal and the noise, but that the paradoxical relationship between trial difficulty and reaction time is caused by the added noise.

Experience-dependent evolution of odor mixture representations in piriform cortex

“…The behavioral setup may be important for setting limits on an animal’s reaction time. Shorter reaction times have been reported in task setups different from ours [ 20 – 22 ], but reaction times were similar to ours in studies with similar behavioral setups as ours, with head restraints and choice reporting using left versus right licks [ 18 , 23 ]. With similar behavioral setups, longer reaction times were also reported in nonolfactory tasks [ 24 , 25 ].…”

“…Previous studies have shown the latency depends on the difficulty of the olfactory task [ 19 , 20 ]. While these earlier studies reported faster reaction times, a recent study [ 18 ] in which mice were trained to report the presence of 1 target odor within a background of other many other odors, reported reaction times similar to those in the present study (approximately 500 ms). The behavioral setup may be important for setting limits on an animal’s reaction time.…”

“…However, in a rodent’s natural environment, odors can be more complex and there may be hundreds of overlapping odors that need to be distinguished from a goal or target odor. Mice can detect the presence of a single odor within a large odor mixture [ 17 ], in a go/no-go design as well as in a left-right alternate choice design [ 18 ]. To investigate how pPC representations change with experience, we developed a complex odor task where mice learned to categorize 1 target odor mixture as different from all the hundreds of other odor mixtures.…”

Robust odor identification in novel olfactory environments in mice

“…Cntnap2 −/− mice have multiple circuit deficits that might affect their capability to detect odors in the presence of strong novel background odors. Although we found that increased variability in the Cntnap2 −/− mice glomerular responses was not large enough to affect classifiers’ performances, increased variability in other downstream neural structures could affect the performance, resulting in the lower performance of Cntnap2 −/− mice 65 . The lack of CNTNAP2 causes a broadening of the transmitted action potential resulting in enlarged neurotransmitter release 66 which might cause excessive activation by strong background odors, masking the target odors.…”

Aberrant circuitry underlying olfaction in the face of severe olfactory bulb degeneration

“…Beyond discriminating odors, the olfactory system also needs to detect and identify odors in the presence of background mixtures. To probe this ability, we tested sFlt1 mice on an olfactory figure-background segmentation task (Rokni et al, 2014; Lebovich et al, 2021). Mice were trained to perform a task, in which they were required to report whether presented mixtures contained a target odorant (see methods).…”