Effect of adaptation on object representation accuracy in macaque inferior temporal cortex

Stimulus repetition produces a decrease of the response in many cortical areas and different modalities. This adaptation is highly prominent in macaque inferior temporal (IT) neurons. Here we ask how these repetition-induced changes in IT responses affect the accuracy by which IT neurons encode objects. This question bears on the functional consequences of adaptation, which are still unclear. We recorded the responses of single IT neurons to sequences of familiar shapes, each shown for 300 ms with an inter-stimulus interval of the same duration. The difference in shape between the two successively presented stimuli, i.e. adapter and test, varied parametrically. The discriminability of the test stimuli was reduced for repeated compared to non-repeated stimuli. In some conditions for which adapter and test shapes differed, the cross-adaptation resulted in an enhanced discriminability. These single cell results were confirmed in a second experiment in which we recorded multi-unit spiking activity using a laminar microelectrode in macaque IT. Two familiar stimuli were presented successively for 500 ms each and separated with an inter-stimulus interval of the same duration. Trials consisted either of a repetition of the same stimulus or of their alternation. Small neuronal populations showed decreased classification accuracy for repeated compared to non-repeated test stimuli, but classification was enhanced for the test compared to adapter stimuli when the test stimulus differed from recently seen stimuli. These findings suggest that short-term, stimulus-specific adaptation in IT supports efficient coding of stimuli that differ from recently seen ones while impairing the coding of repeated stimuli

Effect of Adaptation on Object Representation Accuracy in Macaque Inferior Temporal Cortex

Stimulus repetition produces a decrease of the response in many cortical areas and different modalities. This adaptation is highly prominent in macaque inferior temporal (IT) neurons. Here we ask how these repetition-induced changes in IT responses affect the accuracy by which IT neurons encode objects. This question bears on the functional consequences of adaptation, which are still unclear. We recorded the responses of single IT neurons to sequences of familiar shapes, each shown for 300 msec with an ISI of the same duration. The difference in shape between the two successively presented stimuli,that is, adapter and test, varied parametrically. The discriminability of the test stimuli was reduced for repeated compared with nonrepeated stimuli. In some conditions for which adapter and test shapes differed, the cross-adaptation resulted in an enhanced discriminability. These single cell results were confirmed in a second experiment in which we recorded multiunit spiking activity using a laminar microelectrode in macaque IT. Two familiar stimuli were presented successively for 500 msec each and separated with an ISI of the same duration. Trials consisted either of a repetition of the same stimulus or of their alternation. Small neuronal populations showed decreased classification accuracy for repeated compared with nonrepeated test stimuli, but classification was enhanced for the test compared with adapter stimuli when the test stimulus differed from recently seen stimuli. These findings suggest that short-term, stimulus-specific adaptation in IT supports efficient coding of stimuli that differ from recently seen ones while impairing the coding of repeated stimuli.status: publishe

Prediction-related neural response alterations in the ventral visual stream

Theories of predictive coding (PC; Rao & Ballard, 1999) have dominated neurocognitive research in explaining thought and perception processes in various domains. The basic principle is that perception relies not only on bottom-up processing of sensory input but also on top-down predictions. The current thesis describes several neuronal response alterations in cortical visual areas measured with neuroimaging methods. The so-called repetition suppression (RS) effect was connected to predictive coding as repetitions make stimuli more expected, which results in a smaller prediction error and therefore attenuated neuronal activity. Still, it is questioned whether RS reflects the PE or is a local process by neuronal populations that occurs without top-down influences (Grill-Spector et al., 2006). Another often investigated effect is the reduced neuronal response to expected or predicted visual input called expectation suppression (ES). A considerable body of research on contextual response changes, such as RS and ES, relates to the visual system and the face-processing network in particular. Overall, we demonstrate the importance of stimulus predictability for studies using RS to uncover expectancy-related effects. Furthermore, we suggest that the influence of sensory precision on measures of RS and ES needs more attention in future research. Concerning the stimulus material in the presented studies - unfamiliar, visually familiar, and famous familiar faces - we also emphasize the importance of thoroughly considering the characteristics of faces in terms of prior belief and sensory input precision and predictability when using them for testing prediction-related effects