Top-down effects: examples
 
 
Perception is shaped by one‘s expectation about the acoustic input. Any additional information on the given auditory input can modulate even elementary perceptions. Thus we believe perception to be the consequence of the combination of the input itself (bottom-up information) and the acquired knowledge about the sensory input (top-down information; for a similar view compare Plato: Politeia, „allegory of the cave“). Whatever we hear is interpreted in the light of our past memories, the acquired knowledge about the possible sensory inputs.  

Listen to this example of top-down effects by Drs. M. Davis and I. Johnsrude (Davis & Johnsrude, 2007):








Have you been able to follow? - If not, listen to the original signal:




Examples_files/sws_d3.wavhttp://www.mrc-cbu.cam.ac.uk/people/matt.davis/home.htmlhttp://psyc.queensu.ca/faculty/johnsrude/Examples_files/clear_d3.wavshapeimage_2_link_0shapeimage_2_link_1shapeimage_2_link_2shapeimage_2_link_3
Famous examples of top-down effects exist for the visual system. They are called Mooney figures.

If you cannot identify what is shown here, scroll down.
Knowing the content, the listener will (from now on) easily recognize the original sentence in the previously unintelligible cluster of sounds. Yet the acoustic stimulus itself did not change! It is only that our brain has received some additional, high-level information. However hard we now try to recall the former unintelligible cluster of distorted sounds, we fail. 

Such „top-down“ effects are essentially important for speech recognition in noisy environments.

Read more on top-down effects:
In the deaf auditory system: * Kral A, Eggermont JJ (2007): What’s to lose and what’s to learn: development under auditory deprivation, cochlear implants and limits of cortical plasticity. Brain Res Rev 56(1): 259-269.

In the hearing auditory system: * Davis, MH & Johnsrude, IS (2007). Hearing speech sounds: Top-down influences on the interface between audition and speech perception. Hearing Research 229(1-2):132-47.
In the visual system: * Hochstein, S., Ahissar, M., 2002. View from the top: hierarchies and reverse hierarchies in the visual system. Neuron 36, 791–804.Examples_files/BrainResRev_2007.pdfExamples_files/BrainResRev_2007.pdfshapeimage_5_link_0shapeimage_5_link_1
Decoupling & Prediction codingTop-down_decoupling_in_deaf.htmlshapeimage_6_link_0
Additional information:
Corticicortical couplingsFeedforward_%26_Feedback.htmlshapeimage_8_link_0