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The model of the SC due to Cuppini et al. reproduces development of

  1. multi-sensory neurons
  2. multi-sensory enhancement
  3. intra-modality depression
  4. super-additivity
  5. inverse effectiveness

Enhancement, depression, multisensory interaction on the neural level are mathematically defined by Wallace and Stein as

$$ 100\times\frac{r_{mm}-\max(r_a,r_v)}{\max(r_a,r_v)}, $$ where $r_a$, and $r_v$ are the mean responses to only an auditory or a visual stimulus and $r_{mm}$ is the response to the combination of the two.

Dehner et al. speculate that the inhibitory influence of FAES activity on SIV activity is connected to modality-specific attention: According to that hypothesis, an auditory stimulus which leads to strong FAES activity will suppress activity in FAES and thus block out cortical somatosensory input to the SC.

The responses of some visuo-vestibular cells were enhanced, that of others was depressed by combined visuo-vestibular cues.

The neural response of an SC neuron to one stimulus can be made weaker in some neurons by another stimulus at a different position in space. This stimulus can be in the same or in a different modality (in multi-sensory neurons). This effect is called depression.

Kadunce et al. found that suppressive regions were large and that depression varied depending on position of the concurrent stimulus within the suppressive region. Suppression was generally strongest when concurrent stimuli were on the ipsilateral side.

Kadunce et al. say that two identical stimuli played at different points in space might lead to a translocation of the perceived stimulus and thus to a translocation of the hill of activation in the SC.

Kadunce et al. found that two auditory stimuli placed at opposing the edges of a neuron's receptive field, in its suppressive zone, elicited some activity in the neuron (although less than they expected).

Kadunce et al. found cross-modality depression less often than within-modality depression.

Kadunce et al. found that for the majority of neurons in which a stimulus in one modality could lead to depression in another modality that depression was one-way: Stimuli in the second modality did not depress responses to stimuli in the first.

Kadunce et al. found that SC neurons are very inhomogeneous wrt. to presence and size of suppressive zones.

In the experiment by Xu et al., SC neurons in cats that were raised with congruent audio-visual stimuli distinguished between disparate combined stimuli, even if these stimuli were both in the neurons' receptive fields. Xu et al. state that this is different in naturally reared cats.

In the the experiment by Xu et al., SC neurons in cats that were raised with congruent audio-visual stimuli had a preferred time difference between onset of visual and auditory stimuli of 0s whereas this is around 50-100ms in normal cats.

In the the experiment by Xu et al., SC neurons in cats reacted best to auditory and visual stimuli that resembled those they were raised with (small flashing spots, broadband noise bursts), however, they generalized and reacted similarly to other stimuli.

Stanford et al. studied single-neuron responses to cross-modal stimuli in their receptive fields. In contrast to previous studies, they systematically tried out different combinations of levels of intensity levels in different modalities.

Two superimposed visual stimuli of different orientation, one optimal for a given simple cell in visual cortex, the other sub-optimal but excitatory, can elicit a weaker response than just the optimal stimulus.

In the study due to Xu et al., multi-sensory enhancement in specially-raised cats decreased gradually with distance between uni-sensory stimuli instead of occurring if and only if stimuli were present in their RFs. This is different from cats that are raised normally in which enhancement occurs regardless of stimulus distance if both uni-sensory components both are within their RF.

Neural responses (in multi-sensory neurons) in the sc to spatially disparate cross-sensory stimuli is usually weaker than responses to uni-sensory stimuli.

Responses in multi-sensory neurons in the SC follow the so-called spatial principle.

Visual receptive fields in the sc usually consist of an excitatory central region and an inhibitory surround.

(Auditory receptive fields also often seem to show this antagonism.)

Moving eyes, ears, or body changes the receptive field (in external space) in SC neurons wrt. stimuli in the respective modality.

Anastasio et al. present a model of the response properties of multi-sensory SC neurons which explains enhancement, depression, and super-addititvity using Bayes' rule: If one assumes that a neuron integrates its input to infer the posterior probability of a stimulus source being present in its receptive field, then these effects arise naturally.

Without an intact association cortex (or LIP), SC neurons cannot develop or maintain cross-modal integration.

(Neither multi-sensory enhancement nor depression.)

There is no depression in the immature SC.

Multisensory enhancement and depression are an increased and decreased response of a multisensory neuron to congruent and incongruent stimuli, respectively.

Multisensory enhancement and depression are very different across neurons.

Cuppini et al. expand on their earlier work in modeling cortico-tectal multi-sensory integration.

They present a model which shows how receptive fields and multi-sensory integration can arise through experience.

Bauer and Wermter use the algorithm they proposed to model multi-sensory integration in the SC. They show that it can learn to near-optimally integrate noisy multi-sensory information and reproduces spatial register of sensory maps, the spatial principle, the principle of inverse effectiveness, and near-optimal audio-visual integration in object localization.